Eight hundred years ago, the Culture's intervention in the Chelgrian civilisation went catastrophically wrong, igniting a civil war that killed billions. Now the light from one of the suns destroyed in that conflict is about to reach Masaq' Orbital, and the Culture has invited a Chelgrian emissary to attend the commemoration. Major Quilan arrives carrying a grief that has hollowed him out - and a mission given to him by those who believe the Culture's guilt deserves a sharper answer than remembrance. A novel about the aftermath of good intentions, the weight of grief, and what it means to memorialise a crime you committed while trying to help.