The energy of the Time Lords is being drained by a black hole. A Cosmic Ray Research Balloon brings back a blob of animated energy which dematerializes things on contact. It expands and besieges the Doctor and Jo in the TARDIS. The only way the Time Lords can help is by sending the Doctor's previous selves. The three Doctors discover the incidents are caused by Omega, a bitter Solar engineer trapped behind the black hole in a universe of anti-matter for thousands of years while the rest of his race went on to become Time Lords. Omega wants the Doctor to take his place in the universe so that he can return to ours.  But it is to late - anti-matter radiation has already destroyed the body of Omega, only his will remains and controls his world. Omega wants to destroy the Universe, but the Doctors offer him a positive-matter artifact, thus turning him into a supernova, whose energy will replenish the Time Lords' reserves. The three Doctors return to their rightful places.  The time lords lift their exile sentence. The Doctor is now free to roam Time and Space.  
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The Doctor:  Jon Pertwee
1st Doctor: William Hartnell
2nd Doctor: Patrick Troughton
Jo Grant: Katy Manning
Brig. Lethbridge-Stewart: Nicholas Courtney
Sergeant Benton: John Levene

Guest Appearances:
Omega: Stephen Thorne
Time Lords: Graham Leaman, Tony Lang, Lincoln Wright, Richard Orme, Peter Evans
Chancellor: Clyde Pollitt
President Roy Purcell
Mrs. Ollis: Laurie Webb
Dr. Tyler: Rex Robinson
Palmer: Dennis Palmer
Omega's Champion: Alan Chuntz
Gell Guards: Cy Town, Ricky Newby, John Scott Martin, Murphy Grumbar
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Producer: Barry Letts.
Script Editor: Terrence Dicks.
Writer: Bob Baker, Dave Martin.
Director: Lennie Mayne.
Designer: Roger Liminton. 
Costume: James Acheson.
Make up: Ann Rayment.
Visual Effects: Michaeljohn Harris, Len Hutton
Music : Dudley Simpson.
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Novelised as "Doctor Who - The Three Doctors"  by Terrence Dicks  (0 426 11578 3) first published by Tandem in 1975 with cover by Chris Achilleos.  New edition by W. H. Allen (now Virgin Publishing Ltd.) in 1978 as Doctor Who and The Three Doctors. New edition in 1991 with cover by Alister Pearson.  Target library number 64.

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Released as "The Three Doctors" in the UK August 1991 and in Australia & New Zealand (BBC catalogue #4650). Released in US & Canada 1992. (CBS/FOX catalogue #3405, reclassified as WHV #E1100). Cover art by Alister Pearson

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William Hartnell was ill during filming, and therefore the first Doctor only appears as an image on video screens. This was William Hartnell's last television performance before his death in 1975.

All four episodes exist in color on PAL 2" color videotape, as held by the Film & Videotape Library when audited in 1978.

Ealing filming on Stage 3A. (6 November 1972)
Studio recording in TC1. (27-28 November 1972)
Studio recording in TC6. (11-12 December 1972)
Summerfield Bungalow, Springwell Lane, Rickmansworth, Herts. (7, 9November 1972)
Springwell Quarry, Springwell Lane, Rickmansworth, Herts. (8-9 November 1972)
Springwell Reservoir, Springwell Lane, Rickmansworth, Herts. (7 November 1972)
Haylings House, Haylings Lane, off Tilehouse Lane, Denham Green, Herts. (10 November 1972)

Episode 1 - Dr. Tyler starts to unscrew the top of his instrument package, and before he can finish undoing a single screw, he gets zapped by the anti-matter blob. Immediately after he vanishes, though, we see the lid of the package completely off and lying loose on top of the box, so that the anti-matter blob can emerge.
Episode 1 - Despite the Brigadier claiming that UNIT HQ is a "top-secret establishment", it boasts a large sign outside telling the world not only the function of the building, but the name of the commanding officer!
Episode 1, 2 - The Doctor drives Bessie into the UNIT garage, with Jo holding a large umbrella over them. She folds it up and puts it on the floor in the back of the car. Bessie then gets zapped by the anti-matter and disappears. But in episode 2 when they find Bessie in anti-land and drive off, the umbrella is nowhere to be seen.
Episode 1, 4 - Whenever the scanner is used, it shows a picture of the lab with the TARDIS in one corner. But if the scanner is mounted on the TARDIS, how can the TARDIS be in the picture?
Episode 1, 4 - Several scenes take place in the Doctor's lab with the big chunk hewn out of it. Toward the end of episode 4 it is especially clear that the jagged wall is styrofoam.
Episode 1 - The Second Doctor's recorder can be seen sitting on the console before it supposedly "materialises" and is noticed by the Third Doctor.
Episode 2 - Bessie was supposedly transported into anti-land, but when you first see it sitting there, it has dust all over the tyres as if it had just been driven to its destination.
Episode 2, 4 - You can see the reflections of some camera crew in the monitor used to display the First Doctor.
Episode 2, 4 - When Omega is looking at his "magic screen", you can see the outline of the actual television set at the edge of the image.
Episode 2 - Dr. Tyler tries to escape from Omega's palace, and runs into a Gell Guard that turns to face him, then comes after him. In his haste to get away, he grabs the wall, causing it to wobble noticeably. After he's gone, the Gell Guard then walks straight into the wall!
Episode 2 - After UNIT HQ disappears, you can see grass where it used to be. But how can grass grow underneath a building?
Episode 3, 4 - When UNIT HQ lands on the antimatter planet, the Brig opens the door to see a still photo of a desert CSOed into the scene. Later, when the Doctors and co are trying to get out of Omega's stronghold through the big doors, you can see the exact same CSO shot of the desert outside.
Episode 3 - When the second Doctor, the Brigadier and Benton emerge from the TARDIS, the doors are left completely open with the camera looking straight into them for ages, revealing not only the emptiness of the police box shell, but also that there's a pair of secret doors on the opposite side!
Episode 3, 4 - At various times, you can see actor Stephen Thorne's lips through Omega's mask (and in one profile shot you can also see his jaw), yet when his mask is removed, we find that Omega has been dissipated and has no face.
Episode 3 - The Time Lord President asks the first Doctor to go into the black hole, saying "All three are needed to defeat Omega." Considering that earlier the Time Lords had no idea who or what was attacking them, how did the President learn the identity of the enemy?
Episode 2, 4 - When the Brigadier and co. arrive back at UNIT HQ in episode 4, the TARDIS doors that were left gaping open in the previous episode are now closed and locked!
Episode 4 - As the doors of Omega's stronghold are being pulled open, you can see that the exterior of the doors is smooth and gold-coloured. All of the exterior shots show the doors as being gold, but covered with a rocky texture!
Episode 4 -When the companions are returning to Earth via the pillar of smoke, you can see and hear each person walk up the stairs and then supposedly disappear. Unfortunately, you can then clearly hear them walk down the other side!