A book in Lois McMaster Bujold's Vorkosigan series. This one deals with Mark Vorkosigan, Miles's clone-brother who was created illegally and raised with the intention that he should kill Miles and ultimately take over as Count Vorkosigan. Mark passes himself off as Miles and conducts a raid on the planet of Jackson's Whole to rescue some clones before their bodies are used for brain transplants. It all goes horribly wrong, and Mark spends the rest of the book trying to make up for the damage he caused and find out who he really is.