The Doctor and Jo have narrowly escaped catastrophe after the Doctor's disastrous attempt to seize control of the TARDIS from the High Council of the Time Lords. Having fallen into the custody of non-material beings who inadvertently damage Jo's ability to control her own fears, the two travelers have managed to return to UNIT. But Jo's life and sanity are in danger from the creations of her own mind, and the Doctor himself does not know how to save her. They seek refuge with her uncle over Christmas and meet a strange visitor at the family ancestral home. Meanwhile, the theft of a design for a government security system involves the Doctor in some counter-espionage. Christmas, danger, and mystery! Set after Curse of Peladon. Four Episodes