The Hydrogen Sonata - Iain M Banks (Book 10 in the Culture series)

The Scavenger species are circling. It is, truly, the End Days for the Gzilt civilisation. An ancient people, organised on military principles and yet almost perversely peaceful, the Gzilt helped set up the Culture ten thousand years earlier.

Now they've made the collective decision to follow the well-trodden path of millions of other civilisations: they are going to Sublime, elevating themselves to a new and almost in­finitely more rich and complex existence. But, amid preparations, the Regimental High Command is destroyed. Vyr Cossont, a former soldier for the Gzilt, appears to have been involved, and she is now wanted - dead, not alive.

Aided only by an ancient, reconditioned android and a suspicious Culture avatar, Cossont must complete a ­final mission; she must ­find the oldest person in the Culture, a man over nine thousand years old, who might just hold the key to understanding what happened . . .

The ­final days of the Gzilt civilisation may prove its most perilous.