Travelling with Nyssa in the TARDIS, the Doctor is attacked by a malign entity — a being of pure anti-matter seeking to cross the dimensions. Although the invader is successfully repelled, the TARDIS is immediately recalled to Gallifrey, where the High Council of Time Lords sentence the Doctor to be executed to prevent any further attempts at bonding. It seems there is a traitor on Gallifrey. And what links the Renegade and the disappearance of Tegan's cousin in Amsterdam? Two fates intertwined must battle for the future of the entire universe...