Okay, I have some problems with the basic premises here. Technology for scanning your personality, your soul, and imprinting it on a disposable clay-like… ‘golem’ who is effectively a mental duplicate of you, is so cheap that sending it out to do a classic 9-to-5 job for you will earn noticeably more than the cost of the ‘ditto’. This is complicated by the fact that these dittoes are good for about a day, so doing the above job means a new ditto every day.

All this has profound social implications, which are already in the novel’s past: apparently most of the population is effectively out of work; out-competed by people who can do a few things well enough to be the ‘specialist’ in various mundane tasks and send as many dittoes out as needed to get it all done. There’s still localism, as you can’t do any of this by remote, and in some places they hire a bunch of different people, and in some all the same person. This is discussed some, but not really seen, as the characters involved are all in the realm of the Gainfully Employed.

So, the world building is really what happens to society after this happens, and short of the fact that these golems would have to be impossibly cheap, works well. Meanwhile, the actual plot follows the adventures of Albert Morris, a private eye, over about a four-day period. All the story is told through his viewpoint, or his various dittos’, and uses the device that he habitually records notes of everything as he goes, and everything is pulled from there, or from his own memories. If something happens that those can’t be recovered, then that viewpoint isn’t there.

A hidden question that the book slowly goes into the quality of these duplicates. The bodies range from very cheap and basic, to expensive, with all five senses, better brains, and even being specialized in concentration and the like. But… what if there’s some parts of your personality that just don’t make it over, or only do so sometimes? Albert actually produces very good dittoes, which helps with his work, and so this wrinkle doesn’t show up at first, but becomes gradually more important later.

As a mystery… well, I’m not as much of an expert, but I’d call it good, as things hang together well, and all the twists make sense. The action gets fairly confused during the second half, and especially so at the climax, where there’s a lot going on at once, presented through three different viewpoints (…and things take a turn for the strange). I had stopped paying as much attention to Brin after a couple books didn’t impress me a lot, but this one’s action has me back to wanting to catch up with his writing.