A young man -- who quickly discovers his name is Halloween, and he's a in strange place where disembodied voices and crazy hallucinations run amuk -- works through various onion-layers of "reality" to discover who's trying to kill him. Is it one of his eight classmates, who, like him, have a virtual instructor (Maestro), who seems to becoming increasingly hostile? Or is it Maestro himself? And who is that gray human-shaped phantom who flickers in and out of his reality?
Sagan ably cuts between two storylines: the first one, where Halloween is not only puzzling out the mystery of his and his classmates' circumstances, but the identity of a murderer, whom everybody claims doesn't exist; and the second, where a group of scientists are trying to outrace a pandemic disease (Black Ep) which has a hundred-percent mortality rate, and will certainly wipe out the human race. The two storylines, cleverly woven around each other and full of brainy quips, are suspenseful, with a denouement that ends one chapter of what promises to be a Matrix-style (but better, if Idlewild is any indication) epic trilogy.
Fun, informative (it's full of weird story-enhancing facts), quick-moving and engrossing, this is one of the best science fiction books I've read in a while. Highly recommended, this.
Followed by Edenborn.