Excession — Iain M. Banks

Diplomat Byr Genar-Hofoen has been selected by the Culture to undertake a delicate and dangerous mission. The Department of Special Circumstances--the Culture's espionage and dirty tricks section--has sent him off to investigate a 2,500-year-old mystery: the sudden disappearance of a star fifty times older than the universe itself. But in seeking the secret of the lost sun, Byr risks losing himself. There is only one way to break the silence of millennia: steal the soul of the long-dead starship captain who first encountered the star, and convince her to be reborn. And in accepting this mission, Byr will be swept into a vast conspiracy that could lead the universe into an age of peace...