Mawdryn Undead

At a public school in England, 1983, a school-boy prank goes drastically wrong: Two boys take the Brigadier's classic car for a spin, but end up driving it off the road to avoid a collision. Both are thrown clear. It is at this time that the Black Guardian takes the opportunity to recruit Turlough to the task of killing the Doctor.

Meanwhile the Doctor quickly materialises the TARDIS on board a ship stuck in warp drive to avoid a collision. The Doctor finds a transmat device, and beams down to Earth whilst Nyssa and Tegan follow in the TARDIS. However, whilst the Doctor arrives in 1983, Tegan and Nyssa arrive in 1977.

In 1977 they find a person with serious injuries in the transmat capsule and believe it to be the Doctor suffering from a regeneration. Tegan seeks help, and finds Brigadier Lethbridge-Stewart. At the person's behest they return to the warp craft. In 1983 the Doctor finds Turlough, and a later version of the Brigadier. He tells the Doctor what happened during 1977, but something made him lose his memory. The Doctor, along with Turlough and the later Brigadier, returns to the warp craft.

There they find seven people who tried to turn themselves into Time Lords and have condemned themselves to eternal agony. The Doctor reluctantly offers to help, although it would mean he could no longer regenerate as each remaining regeneration would be used to end a life. However, at the point of transference of energy the energy didn't come from the Doctor, but from the two Brigadiers when they met. The people finally die, the Brigadiers are returned to their time streams. The ship explodes, and everyone wonders where Turlough is, until they find him in the TARDIS.

• Brigadier Lethbridge-Stewart: Nicholas Courtney;
• The Black Guardian: Valentine Dyall;
• Hippo Ibbotson: Stephen Garlick (1-2);
• Headmaster: Angus MacKay (1-2);
• Doctor Runciman: Roger Hammond (1,4);
• Matron (Miss Cassidy): Sheila Gill (1);
• Mawdryn: David Collings (2-4);
• First Mutant: Peter Walmsley (3-4);
• Second Mutant: Brian Darnley (3-4);


• UNCREDITED CAST:
• Mutants: (all 3-4) David Cole, Ian Craig, Mitchell Horner, Michael Leader, Richard Olley;
• Child Nyssa: Lucy Baker (1);
• Child Tegan: Sam Pattenden (4);
• Double for the Brigadier: Richard Sheeker (4);