Castrovalva (TV story)

Castrovalva is a Doctor Who television serial adventure from Season 19. It originally aired in four episodes from 4 January to 12 January in 1982. In this story, the Doctor's latest regeneration has proven more unstable then his previous ones. Adric has been captured by the Master, who is taking advantage of the Doctor's weakened state to ensnare him in an elaborate trap whose  recursive nature threatens to destroy his mind.

Summary
Tegan and Nyssa bring the newly regenerated Doctor to Castrovalva, a seemingly tranquil settlement on a beautifully lush planet in Andromeda, following advice derived from the TARDIS  Information System that "dwellings of simplicity" may have the same restorative effects as the Zero Room, which they were forced to jettison from the TARDIS to escape being drawn into the great hydrogen in-rush known as "Event One." Unknown to them, both the TARDIS Information System and the town of Castrovalva are artificial constructs created by the Master using block transfer computation. Castrovalva is designed to fold back on itself, trapping the Doctor in a recursive warping of space and time which will destroy his already unstable and weakened psyche. Eventually the Doctor and his companions begin to suspect the true nature of Castrovalva, and the Castrovalvans prove so realistic that they become self-aware and also begin to suspect their lives and history are not all they appear to be. A final audience with the Castrovalvan's leader, the Portreeve, reveals that the seemingly kind and wise old man is in fact the Master in disguise. Having kidnapped and used Adric to create his elaborate trap, the renegade Time Lord is now ready to destroy the Doctor completely.

But the people of Castrovalva prove real enough to have wills of their own and rise up in rebellion against their creator. In the ensuing melee, Adric is freed and the loss of the stabilizing effects of his computations causes Castrovalva to disintegrate. The Doctor and his companions manage to escape as the Master, restrained by his own creations, is trapped inside Castrovalva as the city folds in on itself and then ceases to exist. But as the Doctor notes, "The Master never leaves anything to chance..."

Guest Cast
 The Master - Anthony Ainley Head of Security - Dallas Cavell Ruther - Frank Wylie  Shardovan - Derek Waring Mergrave - Micheal Sheard Portreeve - Neil Toynai (pseudonym for Anthony Ainley) Child - Souska John Fourth Doctor - Tom Baker (uncredited)</LI> </UL>