Lois McMaster Bujold: Young Miles

Being a Vor lord on the planet Barrayar wasn't easy. And being the leader of a force of spaceborne mercenaries while maintaining a secret identity wasn't easy - in fact, it should have been impossible, not to mention being a capital offense. But neither impossibility nor danger ever slowed down young Miles Vorkosigan. After failing the Barrayaran Academy physical, Miles' natural (if unorthodox) leadership qualities quickly led to his off-handedly acquiring a space fleet and three thousand loyal troops, and assuming the identity of Admiral Naismith. In short order, he foiled a plot against his father, reentered the Academy, solved a murder, joined a mutiny against a deranged superior, thwarted an interstellar invasion, and rescued his Emperor. Then things got interesting...