In a near-future world, this book tells the story of an autistic man named Lou. Lou seems like a very high-functioning autistic person: he lives by himself, he drives a car to work, where he works with a team of autistic people who do some kind of abstract, pattern analysis or pattern generation that seems pretty technologically advanced and profitable to their company, and he even goes to a weekly fencing group. Early in the book, Lou is thinking to himself (during his required quarterly psychiatric evaluation, where he is careful not to say to much or say the "wrong thing") that "the speed of dark is as interesting as the speed of light, and maybe it is faster and who will find out?" This is a recurring question, which is pretty interesting in itself-- because of Lou's notion that dark must be at least as fast as light, since it is moving ahead of the light to get out of the way; but it also comes to have a larger significance in the book: certainly the darkness hints at ignorance and the unknown, but there is also Lou's discovery that the questions he asks aren't necessarily invalid even though he is "different" and has been told this all of his life.
