The Black Guardian trilogy is composed of three adventures in Peter Davison's second season as the Fifth Doctor: Mawdryn Undead, Terminus, and Enlightenment. The Doctor and his companions are separated when the Black Guardian employs Turlough to kill the Doctor; a space station called Terminus is the refuge of plague victims, dumped there by an uncaring Company, and the Doctor investigates its promises of a cure; and the White Guardian
