简介：Returning to N-Space, the Doctor and Adric are summoned to the tranquil world of Traken, a planet renowned for its peace and harmony. As the Keeper of Traken approaches the conclusion of his millennia-long reign, one of the Traken consuls is poised to ascend to the role of the next Keeper. The Doctor, Adric, Tremas (the Keeper-designate), and Nyssa (his daughter) embark on a mission to thwart the Melkur, a calcified entity deemed a "Source of Evil" that seeks to dismantle the Traken Union. However, they soon uncover a chilling revelation: the Melkur is, in fact, the cunning guise of an old adversary of the Doctor, The Master, who harbors a sinister plan to seize control of The Source (the cornerstone of the Union) and regenerate into a new, formidable form.