In the third episode of the four-part story "Castrovalva," the titular planet has become a temporary home for the TARDIS crew, at least until the Doctor's (Peter Davison) latest regeneration is complete. Unfortunately, Castrovalva is not a planet at all, but instead a huge Block Transfer Computation, created by a brainwashed Adric (Matthew Waterhouse) at the behest of the Doctor's old enemy, the Master (Anthony Ainley). Written by Christopher H. Bidmead, "Castrovalva, Episode 3" originally aired on January 11, 1982. ~ Hal Erickson, All Movie Guide