The Hydrogen Sonata   by Iain M. Banks

An entire, massive, civilization is about to sublime to a higher state of living. In their wake are predators who will be taking their left-over possessions, and the Culture will be overseeing events in order that they may smooth over any ensuing conflicts.

In the final days it emerges that the religious book to which the civilization has held dear through its millennia of existence might have been contrived by an ancient advanced race, and there is one person in the galaxy old enough to remember. But he decided that the memories might cause him more bother than not, and so has them placed in his eyeballs, and then has them removed. They are now jewels in the possession of a rich anarchic member of the subliming species.

And so our protagonist, who happens to have previously met the ancient man, is forced by government to re-assume her role in the military, and embarks on a quest to find the memories, which may have the effect of postponing the subliming, against the wishes of the scavenger species looking to gain in property. And so the scavengers are out to thwart the quest, and the Culture find themselves in a moral quagmire.

This is all so good. The plot runs out on the scale of armadas of system-class warships fighting wars of words and power of the Minds, and on the scale of persons acting within the populations involved; it involves highly modified biological forms, androids, ships’ avatars, drones and knife missiles. There is lots of good action, and a cast of some wonderfully eclectic folk. Some of the scenery defies imagination: a city which takes up the equator of a planet, an airship trapped inside the city which circulates in a tunnel forever, a satellite which flies--below the planet’s surface--inside a circumscribing trench, and more! This is definitely one of Banks’ best.