Parts: 4
Writer: Christopher Bailey
Airdates: 18 January 1983 - 26 January 1983
Production Code: 6D

Doctor: fifth
Companions: Nyssa, Tegan

Creature Feature: Mara

Story: The Doctor is worried when he discovers that the TARDIS is heading toward a different location than he had intended - the planet Manussa, once home to the Manussan and Sumaran Empires. Alarmed by this information, the Doctor remembers that it was Tegan who read him the co-ordinates, and he begins to suspect that Tegan might be under the influence of a malevolent alien force.

At the same time, Tegan is suffering from a nightmare in which she finds herself outside a cave shaped like a snake's mouth. When she awakens, she is filled with terror, but can't remember why. The Doctor sends Tegan into a mild hypnotic state and regresses her back to her dream of the cave. He exhorts Tegan to go into the cave, and when she finally does, she senses another presence there with her. She insists that she will be safe if only she doesn't look at it, but the Doctor tells her she must - and when Tegan turns her head to see, an unnaturally deep voice from Tegan's own mouth shouts at them to go away.

The Doctor correctly guesses that the Mara was not, in fact, banished from Tegan's mind on Deva Loka, but has been buried deeply in her consciousness, gaining power and exerting its control through her dreams. The Doctor and Nyssa hope to find a way to help Tegan on Manussa, where the residents are preparing to celebrate the five hundredth anniversary of the destruction of the Mara...unaware that the legend of its return is more than just a fairy tale. With Tegan under its thrall, the Mara is making plans for its becoming...and it will be a spectacular event indeed.