Doctor Who: Mawdryn Undead (TV)

The TARDIS is trapped inside a huge space ship in perpetual orbit, a permanent prison for the miserable Mawdryn, who tried to steal the secrets of the Time Lords and was condemned to a state of perpetual regeneration. The Doctor's companions are separated from him not in space, but in time. In a timeline chaos, why does the Doctor's old friend, the Brigadier, not remember him at all? Meanwhile, an alien named Turlough living in secret at an English boarding school is contacted by an evil force to trick the Doctor into his own assassination...