I love a good puzzle book, books where often not only the answer has to be deduced from the text, but so has the question. Books like The Quincunx, House Of Leaves and...um... I wish I knew more of them. Anyway, this is one, three linked novellas set on twin colony worlds where identity is fungible and we can't be sure whether the humans are aliens, the aliens are human or if the aliens really exist at all. What does it mean to be alien? What does it mean to be human? Are you a son or a brother or a twin or a clone? Has someone else replaced you or are you the replacement? Is the truth a tool of dystopian oppression? Does slavery set you free? One can have one's head wrecked by a book, be utterly chilled and yet emerged cleansed and confused. Being alive is a puzzle, after all, and we don't want to jump to the ultimate answer too soon.