Someone is taking the Doctor's past selves out of time and space, placing them in a vast wilderness – a battle arena with a sinister tower at its center. As the various incarnations of the Doctor join forces, they learn they are in the Death Zone on their home world of Gallifrey, fighting Daleks, Cybermen, Yeti and a devious Time Lord Traitor who is using the Doctor and his companions to discover the ancient secrets of Rassilon, the first and most powerful ruler of Gallifrey.