For readers and writers, one of the pleasures of series novels that are not also serials is that you can skip around them with no particular concern about sequence or chronology. The world, the universe, where they are set is a given, and you can explore any patch of it you feel like. A random mention, a gratuitous piece of irresponsible world-building, can become in a later book Chekhov's gun, which you hang on the wall in order to fire two acts later. Nothing is wholly serious in such worlds and nothing is so trivial that it can be dismissed from memory.
The vast majority of Iain M Banks's science fiction novels are set not so much in the future but elsewhere, in parts of the galaxy that regard humanity as a slightly embarrassing poor relation. The many species, most of them humanoid, who make up the Culture are intelligent hedonists. Long ago they let most of the actual running of things be done by incredibly intelligent, if whimsical, artificial intelligences, who regard the fleshly beings they protect as quite amusing pets. Some species choose other paths – and collectively transcend into the greater possibilities for wisdom conveyed by the immaterial dimensions of the "Sublime". In The Hydrogen Sonata, this issue becomes crucial.
You might think that to choose a "Sublime" state would be the finest and noblest enterprise imaginable. But for Banks, a writer not unacquainted with cynicism, it is a chance for business as usual. There is here a subset of the detective story where we know who did it from the start; the fun comes from watching investigators uncover what we already know. A politician who has had a crucial role in persuading the Gzilt to "Sublime" learns something he would rather not about his species's past, and specifically about its claims to exceptionalism. He sets out, murderously, to ensure that the last week of Gzilt life on this material plane is not disturbed by this knowledge.
Various Intelligences, accompanied by a young musician who is the sole survivor of one of these purges, try to find out what, and why. We know they will succeed, just as we know that she will learn to play the eponymous piece of music whose difficulty is its only worth.
The fun lies in process: tracking down the oldest man in the galaxy and finding out what he has chosen to forget, or watching the most complicated orgy in history try to break all sexual records. Banks has a taste for the absurd. He will never be sublime but because his gift is, like the Culture's, for having so much fun, he is never bored or boring.
The Hydrogen Sonata By Iain M Banks, Orbit, £18.99 Order at a discount from the Independent Online Shop