Written by one of the giants in Sci-fi, this book was shortlisted for for the 2009 Arthur C. Clarke Award. It stands out for how unique the concepts are and how far out in the future (6 million years) it takes place. It's no small feat to conceptualize some really rich ideas and then carry off a compelling story, but Reynolds does it.
A synopsis of the book would be too long here, but the central theme is around families or "lines" of clones called "shatterlings" (specifically the Gentian line) as they travel the galaxy and come in conflict with other clone lines.
The two Gentian protagonists, Campion and Purslane encounter an emergency distress signal from Fescue, another Gentian shatterling. There was a vicious attack on the reunion world; an ambush in which the majority of the Gentian Line was wiped out. The identity of the responsible party is unknown, but the attackers used the supposedly long-vanished 'Homunculus' weapons – monstrous spacetime-bending weapons that were created ages ago, but were ordered to be destroyed by another Line.
Campion and Purslane now must fight for their very existence within a universe of really interesting ideas and concepts - including the mystery of "the absence" - the complete disappearance of the Andromeda galaxy.
The story has machine people, clones, posthumanism, wormhole travel and more. It's one of the most unique books I have ever consumed. I read the audiobook by John Lee, and I can't recommend that version enough. Don't miss this one.