In remote mountains of Thailand, a secret government laboratory becomes ground zero for a deadly virus. As the virus ravages the surrounding villages, the government imposes martial law, but it's too late. The virus claims thousands of lives in just one week, leaving no hope for a cure or vaccine.

As the infected slowly die and rise again as mutations, the government keeps their disappearance under wraps, and the project is abandoned, forgotten, and left to the virus's mercy.

However, 20 years later, the virus has spread beyond the isolated mountains, and the world is gripped in a pandemic that leaves no hope. The government, desperate for a cure, seeks foreign aid and dispatches a first expedition team to contain the outbreak, but they disappear without a trace. The second expedition team is sent in to find the source of the virus. However, as the team ventures back into the mountains, they realize that the virus has evolved, adapted, and become far more terrifying than anyone ever imagined. What they find there will test their will to survive and may mean the end of humanity as we know it.