Fifteen-year-old Ari Mendoza is an angry loner with a brother in prison, but when he meets Dante and they become friends, Ari starts to ask questions about himself, his parents, and his family that he has never asked before.

A chain of events has been set in motion that will change the Doctor and Peri forever. A chain that involves old enemies as well as old friends. How does Peri come to be the leader of a gang of rebel fighters on an outlying planet? Who is the mysterious 'General' against whom they are rebelling so violently? Where does the so-called 'Supremo', leader of the Alliance forces ranged against the General, come from, and why is he so interested in Peri? The answers lie in the origins of a conflict that will affect the whole cosmos - a conflict that will find humans, Sontarans, Draconians and even Cybermen fighting together for the greater good and glory. For the Supremo. It is a conflict that will test both the Doctor and Peri to the limit, and bring them face to face with the dark sides of their own personalities.