Robin wakes up in a 27th-century clinic missing most of his memories, apparently arranged by his earlier self. After a few weeks of recuperation, he agrees to take part in an experiment, the YFH polity, to recreate a microcosm of the 20th century, an era largely lost to historians.
Robin awakes in a female body called Reeve. (The post-Singularity society has advanced technology which can reassemble human bodies and replicate just about anything you can think of.) Forced to get along in the very conformist society that the experimenters are building, Reeve experiences a reverse Future Shock at life in the dark ages: gender roles, menstruation, biological food, pregnancy!
It gradually becomes apparent that the new world is not as it seems — and neither is Reeve/Robin, when deeply suppressed memories start surfacing.
Stross has put together a fascinating universe as the backdrop to this story, where humans can reassemble themselves at will, back themselves up and have multiple copies running around, and where a long, vicious war was fought against a mind-controlling virus which infected most of the assembler gates. He has fun satirizing some of the norms of 20th century society in the YFH polity. Most of all, he combines an exciting story with some big ideas, the hallmark of good science fiction.