The Tesh and the Sevateem are at war, obeying the orders of their God Xoanon. But they cannot know their battle has a higher purpose, one led by the Time Lord responsible for Xoanon’s condition. A Time Lord called…the Master.
According to one account, the Master had the appearance of Roger Delgado while on Gallifrey. According to another, he had Anthony Ainley's likeness. According to another one, the one with James Dreyfus's appearance was the incarnation who ran away from Gallifrey.
While fighting to extend his life at the end of his regeneration cycle, many bodies were possessed by the Beevers incarnation, but all kept somehow reverting to his real being until he finally regenerated into the MacQueen one. Hence, these sections cannot be strictly chronological
