As a detective story with some way-out elements, this book is great. The central mystery is clever and there are plenty of background questions that are slowly answered. For a long time it's hard to have a clear idea just what is going on at all. Once I was about 1/3 into it I ended up reading the next 1/3 late one night and into the wee hours. There's action on three main time-lines with a couple of others briefly thrown in. 1975 or so is the "present" and there's really only one scene in the future (2058). I remember the 1970's pretty well, so seeing the detectives struggle to gather information and sort it out using what now seems archaic means is entertaining and thought provoking. The casual racism and sexism displayed by some characters is spot-on; not a theme, just part of the background. One intimate pairing is mixed-race, if I read it right ,(not that there are sex scenes of any kind) with no fanfare whatsoever. The family and work struggles presented are realistic and could be out of a novel of mainstream fiction. I enjoyed the book, but it wasn't what I'd been in the market for, which was hard SF.

Barely any 'science' in here, mostly the word 'tachyons' is sprinkled around in the few parts talking about time travel itself, and not in an explanatory way. Some worries about changing history and then statements that history resists change, smooths out the wrinkles. Think H.G. Wells time travel, rather than, say, Stephen Baxter. Why there's an astronaut in a spacesuit on the cover is baffling - there's not a thing about space or space travel to be found anywhere in the book. I almost tossed the book away when one thread veered into a character consorting with Hitler (I'm sick to death of "SciFi" novels that resort to relying on Nazis as easy villains. Lazy! Cheap appeal to the fetid masses.) but I kept going; it didn't get worse and made sense over all. ( )