"The Three Doctors," written by “The Claws of Axos” writers Bob Baker and Dave Martin, was the first Doctor Who storyline to assemble together a group of actors who had played The Doctor in previous incarnations. It also served as the second appearance of The Doctor’s Gallifreyan associates known as The Time Lords who appeared only briefly during Patrick Troughton’s final adventure as The Doctor in “The War Games.” More importantly, the Doctor Who production team finally got the nerve to go back to making alien planets that looked like Studio 54 by giving The Doctor’s TARDIS the power to travel in time and space at the end of this story.
The plot for this tenth anniversary story starts off with some technocolor ooze which makes anything from our fair world (or in DW’s case, England) disappear into an anti-matter universe. The universe is created by the mind of Omega, a former solar engineer and one of the most legendary Time Lords who found himself trapped inside of his own great creation: a supernova that powers the planet Gallifrey. As revenge against The Time Lords who refused to help him escape from his anti-matter universe, Omega seeks to end their existence by draining all of the energy from Gallifrey from the other side of the Supernova.
While exacting his revenge on The Time Lords, Omega goes in search of The Doctor on earth using the technicolor ooze (which Omega created) and some gel-like creatures. Sensing The Doctor would need help against Omega, The Time Lords enlist his first (William Hartnell) and second (Patrick Troughton) incarnations.
After much squabbling between the Second and Third Doctors and a brief recap to The Third Doctor’s current companion Jo Grant (Katy Manning), the ooze transports The Doctor, The Second Doctor, Sergeant Benton (John Levine), Head of UNIT HQ Brigadier Lethbridge-Stewart (Nicholas Courtney), Jo and Dr. Tyler (Rex Robinson), a scientist who was working on the origins of the techno-color ooze into Omega’s anti-matter universe. Omega’s rational for getting The Doctor? To get another Time Lord with an equally powerful mind so that he may take over as ruler of the anti-matter universe in exchange for the freedom of his friends and of The Time Lords.