Doctor Who: The Three Doctors, Episode 1 (1972)

Doctor Who celebrated its tenth year on television with the epochal four-part adventure "The Three Doctors." Attacked by an unknown entity, the Doctor (Jon Pertwee), Jo (Katy Manning), the Brigadier (Nicholas Courtney), and Sgt. Benton (John Levene) take refuge in the TARDIS. Worried that the vessel will not accommodate the Brigadier, the Doctor contacts his home planet Gallifrey for advice -- only to discover that the power of his fellow Time Lords is being syphoned off by a mysterious black hole in space. It is up to the "third" Doctor and his two previous incarnations (played by William Hartnell and Patrick Troughton) to save their species, and, by extension, the rest of the universe. According to legend, this adventure came into being when former Doctor Who star William Hartnell approached the series' producers, asking for a guest spot; though this is inaccurate, it is unfortunately true that Hartnell's illness prevented him from appearing in the same scenes with his successors Troughton and Pertwee. Debuting December 30, 1972, Doctor Who: The Three Doctors was written by Bob Baker and David Martin. ~ Hal Erickson, Rovi