And then, one day, nearly 2,000 years after one man had been nailed to a tree for saying how great it would be to be nice to people for a change things were moving through the ionosphere many miles above the surface of the planet. Several huge yellow slab-like somethings, huge as office blocks, silent as birds, they hung in the air exactly the same way that bricks don't The planet was almost totally oblivious of their presence. They went unnoticed at Goonhilly, they passed over Cape Canaveral without a blip, and Woomera and Jodrell Bank looked straight through them; which was a pity, because it was exactly the sort of thing they'd been looking for all these years