Mark, Mile's new brother wants to be somebody, not only Mile's clone, he also wants to help other clones grown where he was grown, so he fools the Dendarii mercenaries to get a ship and set a mission to save the clones.
When Mile's arrives to the Dendarii and discovers what's happening, he follows Mark and tries to help, but he dies in combat, while still in the battle he is put in a crio-chamber to try to save him later, but the crio-chamber is lost and no one nows where it is.
Finally Mark sets himself as Mark Vorkosigan and discovers the truth about his family, he likes it but not the fact that with Mile's death he would be the successor of count Vorkosigan, so he sets his talents in trying to find and save Miles, wherever he is.
The events finish in a climax which show us another genius in the figure of Mark, so we'll be very happy to read more books with both Miles and Mark, each one with very different talents.