Welcome to this random/miscellaneous/useless information guide where I'll take you on a trip through the Sevastopol station. This is NOT a walkthrough, nor is it a collectible guide. It has trivia, tips, background information, some secrets and some theory. Maybe you were curious about what's behind some door or how the alien would react here and there if you did this and that but were too scared and/or worried about reaching the next save station to find out.

There are some spoilers, so it's kinda assumed you've played through the game already, but feel free to follow the guide on your 1st playthrough as well if you don't mind a few spoilers.

Before heading into the missions, a few general words about Sevastopol and the Zeta Reticuli system you'll find yourself in.

The Zeta Reticuli is a binary star system that also exists in real life. The two stars aren't exactly close. According to Wikipedia, the distance between the two stars is at least 3,750 AU (0.06 light-year, or almost a hundred times the average distance between Pluto and the Sun). (https://en.wikipedia.org/wiki/Zeta_Reticuli)

According to Alien lore, Zeta 1 Reticuli is where you'll find Sevastopol and KG-348, the Jupiter-like gas giant that Sevastopol orbits.
Sevastopol consists of three towers. These are (from the left), Solomon's Habitation Tower, Lorenz Systech Spire and the Sci-Med Tower:



Right in the middle is the Engineering deck/platform and above it the APOLLO core (the stations A.I.).
The three towers are linked by the Towerlink system consisting of transit tunnels (visible in the picture above) and some short-range shuttles.

Zeta 2 Reticuli is where Calpamos is located. Calpamos is the Saturn-like gas giant from Alien and Prometheus. Both LV-426 (the moon from Alien/Aliens) and LV-223 (the moon from Prometheus) orbit Calpamos.

Calpamos and its moons being approached by the Nostromo:



You'll visit LV-426 during a flashback mission.

There's more information about the towers themselves here:

https://steamproxy.net/sharedfiles/filedetails/?id=402866213

The game begins with a cutscene. The year is 2137; fifteen years after the events of the first movie (2122). Amanda Ripley is repairing something (a Lagdamen X34 Land Buggy according to the novelization) while approached by Samuels, a Weyland-Yutani synthetic. The location is unclear, but the novelization says the meeting takes place at the Tranquility Base on the Moon ("Luna"). (The same Lunar base is also mentioned in the Dark Horse comic book Defiance. The Dark Horse books seem to integrate Isolation into their continuity.)

After several weeks of hypersleep, Ripley wakes up on the Torrens. Verlaine and Connor (the ship's captain and navigator, respectively) are the only crew members; the rest are Weyland-Yutani employees. You'll also notice Samuels's.. something (pulse, temperature?) is much lower than that of the others:



All signs above doors and such are from the movie, and each has a specific meaning. See a guide here:

https://steamproxy.net/sharedfiles/filedetails/?id=325588161

This door is sometimes locked, preventing the player from continuing. The only way to fix this is for
the player to restart the game. (Good thing pretty much the only possible softlock in the game is
right at the start. The reactor maintenance section of Mission 14 also acts weird sometimes but
can also be resolved with a reload.) It's a weird bug considering there's no way to close the door in this mission, BUT it is locked by design in the last mission...



The Torrens is an M-class ship, a former "tow rig" like the Nostromo, with two decks, retrofitted for passenger/cargo transport. It still has its tow unbilical, probably similar to the one the Nostromo used for towing the huge refinery (which of course served as inspiration for Sevastopol).

The mission ends with a cutscene. The explosion that destroys the personnel unbilical/EVA line was a trap by Marshal Waits that failed. The scene is played out in Trigger DLC.

This is a good tutorial map, but it's rather painful on further playthroughs because of its highly scripted nature.
You're now in the lower section of the Solomon's Habitation Tower. The upper section (you'll get there later) houses stores, apartments, the Colonial Marshal Bureau and such while this lower section has the spaceport.

The alien will make its presence known for the first time right after you put the power back on in the room with a model of Sevastopol; you'll hear a loud screech. Axel is also around, and you'll probably initially mistake him for the alien:



Once you make it to the baggage claim area, head to the right and you'll hear a cat and the alien in an adjacent room/vent (that doesn't really exist):


Patient Zero (Foster) died on the 14th of November (it's now December). Things seemed more or less normal for a week after that:



These two just keep going at it; nothing happens here until you intervene:



The alien becomes active after killing Axel, but it won't come down from the vents unless you step inside the transit car or make noise. If you make noise, the alien comes down and it seems that it won't leave. Also, after some minutes the transit car will leave and you have to call it back again, which may be tricky with the alien around. The alien will again "activate" when you step inside the car; it's scripted to drop down unless it's already there:

You'll never be able to return to where you were, as that route will remain permanently offline for the rest of the game:



Anyway, welcome to the Lorenz Systech Spire. It houses technological research, server farms and communications.
As soon as you arrive at the transit station, you can actually take another transit to Engineering (a platform in the middle of the three towers); the story won't take you there until much later. There's not much there though aside from some components, but interestingly you can get to the reactor control room and get a good look at the reactor. It's an eerie sight, knowing what's below. No one will bother you here for now:



Then you can take a transit to the middle levels of the Habitation tower. There's not much to do here either, as the doors to the Galleria are closed and the Colonial Marshal Bureau is guarded by looters (and the doors there are locked anyway):



Back in Lorenz, the alien isn't active until a certain scripted sequence, so you can run and make all kinds of noise without fear.
You can kill the looters in the huge lobby; it's easy to lure them into the room upstairs (right above the entrance) and kill them one by one at the door frame. This changes nothing but the fact the alien will not be distracted by them when you return to the lobby later. You can't pick up their revolvers, but that's because this section is meant to teach you about using stealth (plus they want you to witness the alien attacking the looters a bit later):



No matter how far ahead of the looters you are, they'll magically teleport to this doorwar as you descend the stairwell:



The alien is scripted to appear for the second time in the game inside the Tech Support HQ booth (this is where you'll get the revolver), but this is just for show, as the alien won't be active and can't kill you here:



In fact, even after the alien is scripted to elaborately come down from the vent after your interact with the keyboard, the alien won't be active until you use your scrambler to return to the lobby; past this point you should not run or make noise.
The alien may be very active in the lobby and refuses to leave; usually this seems to be the case when one of the looters is still hiding somewhere:



By the way, just because you've pressed a button to take you to the next level, that doesn't make you invulnerable (like it would in most other games):

This is now the top section of the Lorenz Systech Spire; it houses the station's communications systems. The alien isn't around until much later, so don't worry about making noise. The Working Joe androids are non-hostile until you reach upstairs.

After a security checkpoint upstairs you'll be past the public area and the Joes will be hostile, as they're tasked with maintaining the station's communications blackout on orders from Weyland-Yutani.
Hughes gets killed here by a Joe. He is the guy from the Safe Haven DLC; he was trying to re-establish communications:



The doors to the antenna controls & airlock are locked, so don't bother going that way; you'll get there in Mission 16. You can see the Sci-Med Tower in the distance:



If you see Working Joes lying on the floor, seemingly "dead" but with glowing white eyes, then they'll attack you when you get near. You can either walk around them, shoot them (in the head; the white glow will vanish) OR stare at them as you walk by (there's no animation for them initiating attack if you happen to be looking at them).
Note safe:



Safe:



After you manage to contact Samuels with the communications equipment, two Joes make a beeline for your location. It'd have been a cool little detail if these two androids from the small room nearby had activated but instead we get unexplained respawns out of nowhere:



The alien is active on your way back downstairs, past the stairwell, but only in the vents, so don't go underneath them if you spot its drool. If you pay attention to your motion sensor, you can see the alien approach as you go back downstairs. It's safe to make noise as the alien won't come down under any circumstance.

This is probably an oversight by the developers, but the droids cannot follow you past these stairs. OR maybe they're simply programmed to not leave the area and leave it unguarded.



The alien is active back in the Systech Lobby. At the transit station you'll notice two civilians arrive from Engineering. If you attract the alien here (out of spite), they'll probably die.

This is your first visit to the Sci-Med Tower. The upper levels house the Seegson Synthetics plant while this lower section you're in houses the San Cristobal medical center. As you enter the transit station, APOLLO AI shuts down the transit system, locking you in with the alien.

You can kill both Taylor and Samuels. This will lead to a branching of the main storyline.. or you'll just get a game over:



The alien won't come down until he's scripted to do so, that is, after you find the passcode (1702) on the computer and re-enter the hallway. As it's making its slow scripted descent from the vent, you can actually sprint to the locked door and input the code; the alien will be deaf and blind during its elaborate animation.

As a general rule from now on, I'd strongly recommend to never use lockers for hiding! If you enter a locker, the alien will enter a special mode whereby it may come sniffing around your specific locker. If it decides to take an even closer look, you need hold your breath as well (I think it's back+RMB), which will deplete your health. Inside a locker you'll have no control over anything, so it's a matter of luck whether you survive. Obviously the developers never intended the lockers to be absolutely safe, as that'd ruin the game completely. Instead, use other obstacles to hide from the alien. Even a simple crate in the middle of the floor can be perfect for hiding, as the alien's field of vision is rather limited and it seems that "you" is only your head, so it cannot really spot the rest of your body.

In the circular corridor, there's no way to enter rooms A-23 and A-24, so don't bother investigating:



From the rooms within this circular hallway you can view the lobby of the medical center below; you'll find yourself right there in Mission 6:



Doctor Morley got killed in the patient ward. He had been playing chess with one of this patients, but it's implied he was looking for drugs (against Lingard's warnings) and that the patient had been long gone by this point:



You don't have to explore here with the alien around; once you return to Kuhlman with the keycard and the code, he gets up from his chair and exits his room. The alien will then remain in the virtual vents so long as you don't make a noise or meet Kuhlman on the other side of the glass, so the medical is relatively safe to explore at this point.

If the alien is chasing you and you fight it off in the waiting room (with that big window to Kuhlman's room), there's a chance depending on timing that Kuhlman will get stuck sitting in his chair and won't leave, forcing a reload of the game.
If the alien is chasing you or investigating a lure and you face the window where Kuhlman is as he's about to prime the elevator, the alien will vanish (it can't be in two places at once after all).
The alien got behind Kuhlman via a floor vent in his room (you can visit this room later in the game). IN FACT, as a nice little detail, if you quickly rush back to the waiting room while Kuhlman is priming the elevator, not only can you see the vent grate torn open, but the door behind Kuhlman is now suddenly open for a few seconds as well:

You find yourself in the morgue. The alien's behavior here is a bit unpredictable; on two occasions he's been very active and made this section a nightmare (it's very tight), but on most playthroughs it's been in the vents so long as you're quiet. There's a spot behind the table in the middle room where you can hide if you have to (I'd never recommend using the lockers).

Lots of bodies just lying around with marks suggesting the alien simply killed them. Of course, from the movies we know the aliens usually just incapacitate their prey, as killing them would deny the hive valuable hosts.

Past the morgue and into the first vent, you can troll the alien here; it can't reach this part of the vent:



Saving here is a bit perilous, but loading a save always "cancels" the alien and puts it in the vents, so you can't really get softlocked by saving a second before dying. This is useful to know throughout the game (although kinda immersion-breaking).

You can trigger the gas explosion from either side; the alien won't trigger it. You can also just not do it or do it later, as you'll have plenty of opportunities to return to this part throughout the game:



Once you make it to the public section of the hospital, you can kill the looters, attracting the alien in the process, or lure the alien out to kill them (a noisemaker is perfect), or just leave them alive, but then you'd have to deal with them on your way back with all the darkness, noise and the alien drooling in the vents, so better take care of them now.

This is of course Catherine Foster, Marlow's wife, patient zero. She died on 14th of November, 2137. You can see the bloodtrail of the chestburster, leading toward a vent in the ceiling. It's a bit odd they didn't bother to clean it up...:



After picking up the trauma kit, the arrow on your motion tracker will guide you toward the door to the medical entrance, but it's a deadend. You can head straight for the emergency shutdown machine instead. The game is good that way; many other games would've insisted that you make the pointless trip first.

The alien becomes kinda inactive once you've locked yourself inside the emergency shutdown room; it'll stalk the overhead vents though and it will come down if you make noise. Once you activate the machine, you can leave the room either via the door or the vents.

The Joe does its little Ash imitation:



The pre-rendered cutscene will immediately despawn the alien if it's behind you.

You can see Mission 5 rooms above. This room will also slowly drain your health (this should've been made more obvious), so be mindful of that:

This is the synthetic storage section along with an operating theater for aspiring android technicians. The alien will be immediately active and come down if you make noise, but otherwise it'll linger in the vents.

You can keep the looters alive if you're a misguided pacifist. I suggest first getting past the operating theater, then tossing a noisemaker at them and have your alien companion finish them off.

It's not immediately clear whether this Joe was destroyed by the looters or the alien. Aliens may attack androids if they get in the way (remember Bishop?), but these are programmed to protect the "specimen", not interfere. Remember how Ash's head seemed to come off pretty easily in Alien, so this could've been the work of the looters:



The log mentions "120-A/8", which is a Hyperdyne Systems Weyland-Yutani android model. For reference, Ash is an older model 120-A/2 and Bishop (still decades away at this point) is 341-B:



"No wonder Seegson is losing the tech race" indeed.

The Joe in the large storage room will open the warehouse for you, but if you kill it before it opens the door, you can still loot the body for the key:



The Joe is then scripted to walk over the electrified floor and die, but you can actually save the Joe by taking the route on the right side of the room, then turning off the electricity. The Joe will then return to his pod (but without actually getting back inside) in the large synthetic storage room:



The alien will despawn from the mission once it nabs one of the civilians; presumably it's on its way to the hive with its catch:



Don't shoot the civilians here, by the way, as they're non-hostile. I actually realized this only on this playthrough, having always killed them or avoided them on previous playthroughs (I took pride in how stealthy I was in approaching them). Too bad they have no reaction to you:

The alien won't be active here. However, if you switch maps and return to Medical Staff Entrance or Seegson Synthetics via the elevators, the alien will be active but doesn't seem to come down unless provoked. It'll be the same if you head for the Systech Spire or Engineering.

In the transit command you can see a map of the Towerlink Sytem. The one at the top of the Systech Spire probably refers to the short-range shuttle bay you find yourself in at the start of Mission 16; it's clearly labelled as being part of the Towerlink System in that mission:



Once back at the transit station, you can hide in the lockers and wait for the looters to leave or you can engage them. An easy way is to throw a pipebomb when they're grouped at the bottom of the stairs, or use a flashbang, then the revolver.

This is by the far the most linear mission in the game. It's cool the first time around but dreadfully boring on further playthroughs. It doesn't really seem to have anything fun to discover either; I kept looking at the rocks outside waiting to see a fossilized Space Jockey inside one of them (this is something they intended to film for Alien at one point) - but no luck.

You can race your colleagues for the derelict by walking in a straight line:



The question on everyone's mind since Alien, is this huge cavern a part of the derelict or underneath it (or a section of the ship that we don't see from outside)? In the original script ("Starbeast") there was a separate structure (a temple/egg silo) that housed the eggs, located some distance from the derelict. It was cut out of budget considerations, but its inclusion might have implied an altogether different origin for the eggs (rather than a Space Jockey/Engineer ship with a cargo of bioweapons). Still, the architecture seems to be that of the Jockeys/Engineers, so I'll say the cavern is a part of the derelict:

Waits had three traps (one left by this point) and each almost killed Ripley:



You can kill the civilians here, but then you'll get a game over:)



As a sidenote, if you take a trip to Engineering, the alien will be active there, but it will not react to you if you make noise within this corridor (behind you is the control room overlooking the reactor):



You need to get its attention outside this corridor, then have it follow you (have your flamer aimed at it but without firing). If it gets stuck behind a door, it'll despawn. Similarly it'll despawn if you blast it away here, implying it's not mean to be in this section:



You return to the Lorenz Systech Spire. Right before the lobby there's an explosion if you decide to check out the room labelled "Security". The explosion won't alert the alien, but a burning Joe will emerge from the inferno. Engaging the Joe will alert the alien, so simply wait for the Joe to burn to "death" in the nearby vents. Note that being in the burning rooms drains your health, so activate the sprinklers:



As a small made-up "sidequest" (the game has literally none, thank god) you can rescue some civilians here by alerting them of the alien being around. There are two civilians in the lobby (hard to miss them), one in the cafe above (take the left stairs) and last one (who'll reward you with a passcode) in the System Monitoring room behind Tech Support HQ (this is where you found the pistol in Mission 3). The first three will leave via a door labelled "Staff Acccess Only" (and no, you can't go there):



As an option, you can take the main elevator in the lobby and explore Seegson Communications (remember Mission 4?); all Joes there are gone now, and you can get the first Nostromo log easily plus open up some vent routes for later use. The alien will be in the vents, so don't make noise. HOWEVER, if you decide to go all the way up the stairwell, then up the elevator to the large communications room (not sure why you'd do that, as there's nothing up there), then on your way back down three looters might appear near the security checkpoint (where you witness Hughes get killed by the Joe in Mission 4). I fought them with the wrench (the location below is where Ricardo will later sit on that chair), and that did not attract the alien:



Moreover, there were three more waiting by the elevator to the Systech lobby. These actually killed me without the alien ever paying attention. When I loaded a save the looters were gone but the alien was in the vents and receptive to noise, so who knows what's going on in this section:



Back in the Systech lobby and continuing with the mission, you go up the stairs and then enter this familiar stairwell (looking toward Habitation):



For some very weird reason Ripley makes all kinds of sounds of fear and distress when you quickly move your mouse in a specific way to the right while staring outside toward the Habitation Tower. A weird bug indeed. What could explain it? (One section of the vent near the burning Security room also exhibits similar behavior; in terms of geometry it's quite close to the stairwell.)

You can trap the alien inside this; simply lure it in with a flare or a noisemaker, stay hidden in the adjacent vent, then activate the shutter (watch the tail!) while it's investigating the lure. It'll stay trapped until there's a reload of the map or you continue with the story and the alien's presence is "required" by a scripted sequence. Don't get too close though, as the alien will kill you through the shutter:



The Joe here will become hostile if you get in its way, by the way; dealing with it will be tricky with the alien around.

You can shoot these pipes in the server room and they'll burn, kind of a weird little detail:



The alien can be annoyingly active in the Gemini labs, but on some occasions it's been less aggressive, so its behavior is not set in stone here. Just don't let it get any reason to come down. Watch out for the security cameras and avoid the Joe. This is definitely one of the hardest parts in the game.

You can see the two detachable laboratory modules through this window:



The module is also a great place to see some of the many moons orbiting the gas giant:



This should 100% kill you (also, the module is spinning, so she wouldn't be ejected in a straight line anyway):

The alien will be absent for three missions now. The Joes have left their posts and ordered to kill everyone to protect the specimen (that you just killed).

You can now enter the "mall" section of the Habitation Tower (this is where the station's inhabitants eat, sleep, shop, etc.), but you cannot re-enter the section where you and Axel where chased by the looters and the alien.
The baton is very useful against the Joes (basically a one-hit kill, as you hit them once, then finish them off with the wrench), so I hope you practiced your timing (all weapons are kinda clunky in this game by design). Let the Joes deal with the looters (although they'll kill innocent civilians as well). You can try to save the civilians by killing the Joes quickly, but in the long-run they're dead anyway (aren't we all).

If you decide to freeroam, be warned that Joes will have spawned at and around transit stations as you move around. I spotted one upon arriving at Systech, then another in Engineering, and two Joes hang near the Gemini/Project KG348 elevator:



The shutters in Project KG348 are closed now, but they forgot to remove the detachable (and now gone) module from the skybox:



Almost had a heart attack here (Gemini lobby where a woman sits on a couch looking outside - if she survived Mission 10, that is); you can hear the alien's attack sound twice here, first as you're about to enter the corridor and then within the corridor. The creature itself isn't around, however. Either it's an intentional clue that aliens are still around OR it's just an oversight; but if it's the latter, it sure is a weird one:

This guy, Smythe, will be mentioned in a computer log later. He wasn't here the last time you visited this area in Mission 7. This is an obvious reference to the Ash/Ripley fight in Alien:



Did Ripley get scared of Samuels here or why she didn't attempt communicating with him/it. She knew of him ("it" more like) being an android, but maybe this shocking display of violence got her scared:



You can see the transit bridge to Apollo Core here:



As you can see on the map, it's part of the Upper Transit system. It's somewhat unclear where exactly the core is, but it has to be right above the Engineering deck (which in turn is right in the middle of the three towers):

You hate to give all of this stuff away, but don't worry; they'll be magically available later in a totally unrelated location:



I really wouldn't waste components (aside from flares) on the Industrial Joes here. There are environmental traps to kill them on both sides of this symmetrical map. Work your way past the data banks, get to the computers without being detected, then operate the traps.

The insides of the APOLLO core are obviously influenced by the MU/TH/UR room from Alien.

Purchased orders recieved... Not one by two typos by an AI... In any case, it seems Weyland-Yutani bought the facility a week after Foster's death by the chestburster:



Ripley tries to tell the AI the creature is off the station but is told data from the reactor core might contradict her claim:



Ransome is worried about W-Y learning about the disappearances, as if that might sap the company's appetite to buy the station. Little did he know about their true motivations...:



Apollo Primary Interaction Log entry on the computer shows plenty of interesting data (copied from https://gamefaqs.gamespot.com/ps4/751154-alien-isolation/faqs/70566):

11/11/2137

Class: Human interaction
Request for inter-corporate messaging received. Outgoing message to Weyland-Yutani representatives accepted and monitored.

11/16/2137

Class: Colonial Marshal Incident Report
Temporary emergency measures initiated in San Cristobal Medical Facility. No further information provided.

11/17/2137

Class: External interaction
Purchase order received. Weyland-Yutani operational ruleset packet received, verified and installed.

11/23/2137

Class: Colonial Marshal Incident Report
Emergency measures initiated in San Cristobal Medical Facility extended. No further information provided. Station scans initiated under WY directive #00043b56.

11/24/2137

Class: Containment Hazard Alert
Unverified scans in Reactor systems. Special Order 939 initiated. Priority One. Protect Specimen. Maintain station quarantine. Disallow communications.

12/11/2137

Class: Sevastopol Arrivals Log
New inhabitants logged with Apollo systems by synthetic staff. Ripley, Amanda. Level 2, Weyland-Yutani. Taylor, Nina. Level 4, Weyland-Yutani. Samuels, Christopher. Level 3, Weyland-Yutani. Expendable.

12/11/2137

Class: Containment Hazard Alert
Viable threat to specimen detected in Project KG348 Hazard lab. Containment Hazard Alert raised to Omega.

It seems the effort to kill the alien made the A.I. unleash the Working Joes on Sevastopol's human population.

So right below the APOLLO core is the Engineering deck/platform.

This is like the room in Alien with all the vehicles and equipment, adjacent to the landing leg chamber where Brett was killed:



So that's what the tracker was intended for, to track vermin. Good thing the one Ripley is carrying seems to have been modified to ignore such noise:



Reactor Maintenance at the bottom of the reactor is where the aliens have set up a hive. We don't see the queen, but the developers have confirmed its presence. This begs the question: Was the chestburster that came out of Foster a queen? That'd be too convenient, not to mention queens rely on others to bring them hosts and such (but are they active hunters before they start laying eggs?). The first drone could've used the so-called Eggmorphing technique (seen in the director's cut of Alien) to bring in more aliens.
Maybe the aliens can even decide which facehugger lays the queen embryo in a way similar to how honeybees can bring about queens by feeding the right amount of royal jelly: https://en.wikipedia.org/wiki/Royal_jelly

This section bugs out sometimes, by the way. There'll be no sounds, items are floating, etc. A rather weird way to fix it is to take the elevator back, change your resolution, then head back down, then change your resolution to whatever it was.

Once inside the hive, scavenge the bodies you see cocooned to the walls and shoot any eggs before they hatch. With good timing you can kill facehuggers with the wrench (it's not as tricky as it sounds), but you'll lose a bit of health (due to acid) and this is NOT a silent way to kill them (there is none). Also, be aware that you cannot swing the wrench in the small tunnels/vents that you'll come across in the hive.

The aliens (there are two even though the tracker gives the impression of many more) become active the second you overload the first core. However, if you make no noise then the first one will appear when you make it back to the save point, but another may still randomly fall down from a vent above Alpha core:



With some luck and by being stealthy the second alien often won't come down until you reach the second save point.

This is some kind of a deadzone where ambient sound effects stop completely:



There's nothing terribly interesting at the end of this corridor, just some components. Feel free to ignore them unless you're a completionist:



Fake urgency; wait here for the screaming to stop:



These tunnels are also a kind of a deadzone. The aliens can't enter these. You can even shoot them. They also don't react to any noise you make within these "vents":



Once you purge the nest your tracker shows plenty of aliens all around, but this is just for show: The aliens are actually totally inactive until you get to the next mission (and leave Seegson Communications):

The alien won't enter the Transit Control (from Mission 8). It'll audibly react to any noise you make but can't come down despite there being two vent openings in the large room. It also can't enter the corridor nearby (after the small elevator):



The lone Facehugger here has always seemed a bit weird. It must be the one that was on Foster; it's even described in the computer log right next to the facehugger. Seems a bit far-fetched to believe it's a stowaway either from LV-426 or Sevastopol. Maybe some have it in them to plant two embryos, like was implied in Alien 3 (but not in the so-called Assembly Cut, which had a specific "Queen Facehugger"; but that version is a mere curiosity, not endorsed by the director):



"Safe to assume it isn't a zombie"

Foster was put in a hypersleep after the Facehugger had finished its job. On approaching the station she woke up in terrible condition. She died four days later; it's not specified whether she was kept in stasis or sedated. The alien's gestation time is always convenient to the plot, ranging from less than an hour (AvP, Romulus) to several days (Alien 3):



Note the computer screens say LM-link when booting, not Sevastolink.

The place seems to have a lot of bunks. It's a salvage ship (remember Ellen Ripley was rescued by one decades later), so maybe they're in case they find entire crews rather than just scraps floating in space:



Don't go into the light:



Stay here for too long without doing anything during the button puzzle and the place will blow up, killing you. The same during the escape sequence. Still, the urgency is mostly make believe: you can actually simply walk your way to the exit. There seems to be some counter that starts from zero every time you enter a new area.

Your short-range shuttle took you to the top of the Lorenz Systech Spire rather than back to San Cristobal. The station's orbital stabilizers were destroyed by the Anesidora explosion, meaning there's no force to carry the station "over the horizon", leaving it falling into the gas giant's atmosphere.

This is known as the ideal moment to go back to previous locations to look for remaining collectibles (Nostromo logs and id tags), as everything will be open to you. The alien (there's just one at a time) will be mostly in the vents but may sometimes come down at random even if you don't make any noise. Sometimes it'll be some distance away so that making noise will bring the alien down with considerable delay; it's got great hearing as well! Sometimes the tracker puts it in vents right above you but it doesn't make any sound and takes a lot of time to get to you.

The cafe/lounge in the Systech lobby - the alien seems to be flying in space:



A Brett Nostromo log in Engineering, fittingly in the vehicle room that looks like the place where Brett came across the chestburster's skin in Alien. The code on the whiteboard is an obvious reference to the release year of the movie. Harry Dean Stanton sounds a bit old here, but then again he was approaching 90 and Isolation was one of his last appearances:



The alien's behavior is a bit wonky in Engineering. I'm not sure if it was ever "optimized" for that location, as you'll never come across it naturally there, only during optional backtracking. Toss a noisemaker over the boxes and the alien will get stuck here. Shoot it and it'll disappear straight up:



You can revisit the reactor also but not reactor maintenance where the hive was (Ripley did something to it that neither Ricardo nor myself could quite understand). The alien won't bother you in the large reactor room.

A Weyland-Yutani ad in a transit car:



Thedus was mentioned in Alien, but only in the theatrical version. In the theatrical version Dallas mentions to Ripley how the Nostromo's usual science officer was suddenly replaced with Ash "two days before we left Thedus" (presumably the mining planet where they got the huge refinery from). This was cut from the director's cut probably to keep Ash's identity a total secret:



Back in San Cristobal, feel free to visit Kuhlman's room now. You can see the vent the alien come from; although it doesn't really seem like it could've squeezed through that hole, but whatever, I guess they had settled on a fixed vent size in this game:



There are some looters in baggage claim (Habitation Tower), near where the cat was killed off-screen in Mission 2. This time they gave me a heart attack, as I don't recall seeing them before. Anyway, toss a noisemaker and let the alien take care of them; if you engage them directly, you're gonna have to deal with the alien as well. The shotgun from Mission 11 seems to be here again along with the pick-up animation:



You can now get to Mike Tanaka's room nearby. He seems to have been a gifted artist. The code to his locker is available on Twitter (@miketanaka2095): it's 2931. As far as I can tell, it's not mentioned anywhere in the game. The twitter (still available) is a useful trove of information about the downfall of Sevastopol:



You'll come across many higher level schematics. They're mostly worthless, even downright harmful. For example, third level molotovs and pipebombs start emitting noise when placed on the ground as traps, a useless feature. After all, if you want to attract the alien, all you need to do is hit a wall with your wrench. The attached noisemaker means you can't use them as a safeguard (in case the alien gets behind you while you operate the ion torch or something like that).

Watch out, Betamax, you have a competitor:



Back to Mission 16 and Seegson Communications. The place is crawling with heavily armed (and armored!) looters, the top brass of Seegson Security. I'd strongly recommend dealing with them now, as the alien will be absent from this section for now; they'll be a pain to deal with when the alien is around as well, making this potentially one of the hardest sections in the game.
You can simply lure the guys into a pile with a noisemaker and then toss a grenade at them:



Or you can sneak around them and free a captured Industrial Joe and watch him kill everyone. You can free the Joe from his tiny room by operating a computer here:



When the Joe is released, don't let it see you:



The door leading to where you managed to contact Samuels and Taylor in Mission 4 is closed, so don't bother investigating:



Confirmation that it's December 11, almost a month since the first alien burst out of Foster:



Solomon's Habitation Tower is on the right, the smallest of the three towers:



The Sci-Med Tower is on the left, the second highest tower:



Look up on your way back inside; you can see the alien crawling along the wall, then disappear above the large Seegson Communications room:



It's never happened to me, but I've seen some get stuck with the spacesuit on after their spacewalk, having to drag it all the way to the next mission (by which point it should disappear):



The alien you just saw outside the station jumps in from a vent above and causes decompression, causing window shutters to close down:



It'll fight the looters if you didn't kill them.

On your way back down the elevator you'll notice the alien following on your motion tracker. It's then scripted to appear in this vent to your left as you step out of the elevator:



You can shoot at it and make all kinds of noise; it won't come down until it's scripted to in the next area after you find Ricardo with a Facehugger on him.

I hope you killed (or had the Industrial Joe kill) the looters downstairs, otherwise this section can get tough with both the looters and the alien around.

This Upper Transit station will take you from the Lorenz Systech Spire back to the Habitation Tower. The Towerlink system has been shut down by Sinclair, so you're gonna have to put the power back on:



Once inside the car, the alien will follow you via the transit tunnel; you can track its movements with the tracker when inside the car:



You can actually see the transit tunnel you're currently in from this familiar window in the stairwell near the Systech lobby:



The area of the Habitation Tower you find yourself in is the so-called Sanctuary that's been mentioned several times in the game's computer logs. This is where Sinclair and his Seegson Security goons barricaded themselves in. You'll notice it didn't stop the alien(s). Maybe they forgot to look up? Should've watched the movies...

Inside the Sanctuary there are several scenes where the alien despawns and won't come down from its virtual vents until it's set to make some dramatic scripted entrance. For example, when you're expected to input your keycard here, the alien will be harmless until you interact with the key lock:



Escape pods. Did anyone try using them? Of course, with communications shut down by APOLLO, the idea of floating in space in a tiny pod must not have seemed that attractive:



Once you interact with a lever in the room with the air hockey kind of table, the power shuts down and you'll hear numerous aliens screeching somewhere.

Sinclair dead. He and his goons killed civilians, so don't take pity on him:

You're back in the Spaceflight Terminal, emerging from underneath rubble that was conveniently inaccessible before. Remember there's a Nostromo log here.

The spaceship maintenance control room seems quite similar to the Seegson Communications room, but they serve rather different purposes:



There's one alien here, so try not to make noise.

You've probably come across several similar locations throughout the game:



These are deadzones as far as the alien is concerned; the alien won't react to any noise you make within this sector, not even if you toss a noisemaker outside the deadzone. HOWEVER, if the noisemaker is still emitting noise when you leave the deadzone, the alien will come immediately.

Personnel unbilicial is gone; in fact, it seems to have been decommissioned more than two months ago:



Ripley gets the idea to use the maintenance rig instead (used to repair ships).
Once you've extended the maintenance rig and make your way back toward the stairwell, another alien will spawn. This is the second time that you have to deal with two aliens at once. There won't be much space to move around, but with your equipment you can simply fight the aliens and make a beeline for the airlock:



After a cutscene Ripley finds herself... somewhere. The location is a bit hard to pin down, but it's several floors above where you just where. The recreational room you're in is in the process of being turned into a makeshift hive; the Queen is presumably cooked by this point, so the aliens need a new hive (and would have no knowledge the effort is doomed).

Your motion tracker is picking up lots of signals but there are no aliens here aside from a single scripted scene:



Now, some have speculated that Ripley was impregnated during her blackout, but there are several reasons to think she wasn't:
-There are no dead Facehuggers next to her. Of course, they could be anywhere (the one in Alien hid after it had finished its job, remember?). But there's an unhatched egg right next to her:



-More importantly, you'll come across many Facehuggers that will try to attack you.
-Even more to the point, the two aliens in the broken transit car will attack you (you don't even need to be aggressive; just make your presence known to them), as will the ones near the end as you're trying to release the docking clamps AND the final one on the Torrens:



-Lastly, there probably isn't enough time (even though the time it takes to implant an embryo is one of those things that's determined by whatever is most convenient to the plot). While we don't know how much time passed, it couldn't have been hours.
The exact spot you're in when the aliens appear in the transit tunnel is unreachable to the two aliens as it simply doesn't accommodate their AI (it's neither a vent nor a room). This must've confused some into believing the aliens won't attack you, even though all you need to do is move toward the closest alien and it'll immediately kill you.

What's the point of putting these eggs here:



Once you're on top of the Torrens, you'll see an alien observing you on the maintenance rig. Another will appear soon. If you take too long here the aliens will kill you. It's not clear why they won't attack immediately, but it's probably an allusion to the end of the first movie and to add a bit of tension (you don't have any weapons, after all):



Sevastopol freefalls into the gas giant's dense atmosphere and is destroyed:

Ripley is back on the Torrens. It seems the ship has more than a single airlock, the second one being on another deck (Amanda spawns at the bottom of a ladder). Remember the Torrens is an M class starship just like the Nostromo, which also had more than a single airlock.

An alien is behind the door that takes you to the mess. Did Verlaine and Carter die? The bridge door behind the alien doesn't seem to be locked, as the light on it is green:



But there's still one more door behind that. Remember she couldn't reach them seconds ago. It's not clear if the alien got aboard the ship roughly at the same time as Ripley or much earlier, somewhere between the maintenance rig being extended and Amanda entering the airlock. How it got in is another matter, but maybe they're like flies in that they always seem to find some way inside...

The alien will kill you if you fail the extremely difficult QTE that essentially functions as the game's final boss battle:



Ripley is then seen floating in space. She's alive and found by a ship, but piloted by whom? It could be Weyland-Yutani (their ship probably took off the second they heard of the alien being on Sevastopol), it could be the Torrens, or it could be any number of other ships making a stop at Sevastopol.

In Aliens Burke says Amanda survived until old age. He could be lying, but it's not implied. In the Dark Horse comics (Resistance and Rescue, the last issues before Dark Horse lost their license to Disney) she returns and three years later teams up with Zula Hendricks, a marine, and goes on a rampage against Weyland-Yutani:



The novelization ends a bit differently. While floating in space, Amanda finds a communications beacon and starts transmitting a signal, hoping a nearby ship would receive it. She spots an alien on another floating piece of debris further away, but the alien is completely static, as if asleep.

That's about it. Feel free to comment especially if you feel like I missed something important; I'd be more than happy to keep updating the guide.