136 Apollyon part four

REGENERATION The Great Key has been returned to Gallifrey, but not before the Doctor sacrifices his life in a climactic battle with the Master. While the Doctor tries to recover from his latest regeneration, the Master seizes upon the opportunity afforded by the Doctor’s confusion and new appearance by switching bodies with him — the Doctor’s mind in the Master’s body and the Master’s mind in the Doctor’s — and returns to Gallifrey in a bid to take over the High Council Presidency and retrieve that which he lost: the Great Key.