The Five Doctors (1983) watch online

"The Five Doctors" is a special feature-length episode of the BBC science fiction television series Doctor Who, produced in celebration of the series's 20th anniversary. Written by Terrance Dicks and directed by Peter Moffatt, the episode first aired in the United States on 23 November 1983, the anniversary date, and aired in the United Kingdom two days later. Peter Davison stars alongside returning actors Patrick Troughton and Jon Pertwee. Richard Hurndall portrayed the First Doctor, as original William Hartnell had died in 1975. Tom Baker declined to appear, so his absence was covered with footage from the unfinished serial Shada.

In the episode, the Doctor's first five incarnations and several of his companions (Janet Fielding, Mark Strickson, Carole Ann Ford, Elisabeth Sladen and Nicholas Courtney) are displaced from different points in time and transported to Gallifrey. They are forced to navigate various foes within the Death Zone, including a Dalek, Cybermen, Yeti and the Master, in order to uncover a Time Lord plot to access the secret of immortality.

Source: Wikipedia (CC BY-SA)