A non-Culture SF book by Iain M. Banks. According to something I read online there were some claims by non-M fans that this should have been an Iain Banks novel, becase it was mainstream not SF. Clearly the Margaret Atwood school of genre-definition – if it doesn’t include spaceships and space squid then it’s not SF. Rubbish of course. While a non-Culture novel, this is an SF novel in a grand tradition. Parallel universes have been a staple SF trope for many years. There are more than a few hints of Richard Meredith’s Timeliner Trilogy here, though with Banks’ take on it. There are multiple viewpoints, though only one told in first person, the rest in over-the-shoulder third person. There’s a complicated temporakl structure with flashbacks and time-skipping (of some kind, perhaps just moving to a near-identical parallel world which lagged behind the rest in time progression). This jumping around in time and viewpoint is perhaps a little over-contrived to turn what is actually a fairly simple story into something more complicated. Worth perservering with, but not his best non-Culture SF novel.