Serial: 6S  Episode Nos. 631, 632, 633, and 634.  Title: The Twin Dilemma

The Doctor emerges from his latest regeneration very disturbed, to the point where he nearly murders Peri.  Appalled by his actions, he decides to become a hermit, and takes refuge on the barren planet Titan 3.  Nearby, however, is a base hiding an old Time Lord friend of his who has been forced to abduct twin genius children from Earth to aid the scheme of the alien menace that now controls his adopted planet.  Will the Doctor recover his sanity in time to rescue the children and his friend?

This story sees the debut of Colin Baker as the Doctor.

starring Colin Baker as the Doctor, and Nicola Bryant as Peri. Written by Anthony Steven, Produced by John Nathan-Turner, and Directed by Peter Moffatt.

Originally transmitted from 22 March 1984 to 30 March 1984 on BBC1.