[[caption-width-right:350: Two Doctors are better than one. (When they aren't bickering, that is. Then you need a third one on a fuzzy monitor to break them up.)]]
->''"So you're my replacements -- a [[Creator/JonPertwee dandy]] and a [[Creator/PatrickTroughton clown]]!"''
-->-- '''The First Doctor'''

The one with killer pixels and the Doctor arguing with himself.

The [[MilestoneCelebration tenth anniversary]] episode of ''Series/DoctorWho'' was marked with the first "Multi-Doctor" episode, a concept which would be used several more times over the coming years.

The Doctor is investigating the appearance of a mysterious blob-like creature which, it transpires, is hunting him down. Reluctantly, he calls on the Time Lords for help. Unfortunately, they're a bit preoccupied with a black hole draining all their energy, so they send his past selves over to help. The Second Doctor appears in the Third Doctor's TARDIS, and the two of them immediately proceed to bicker LikeAnOldMarriedCouple before grudgingly opening up a psychic link ("Contact!") between them. The First Doctor is caught in a time eddy and can only advise via the TARDIS viewscreen, but he deduces that the blob creature is a "time bridge". The Third Doctor and Jo allow it to capture them and they are transported to a world of antimatter beyond the troublesome black hole.

Meanwhile, back on Earth, the Second Doctor, the Brigadier and Sergeant Benton take refuge in the TARDIS. The Brigadier flat-out refuses to believe anything that's going on, and the Second Doctor trolls him mercilessly. The First Doctor tells the group to switch off the forcefield, and the TARDIS (and with it the UNIT HQ) are all transported to the antimatter world.

It turns out that the problem is Omega, a renegade Time Lord. Omega was a stellar engineer, and his experiments enabled the Time Lords to develop time travel. But one of his experiments went wrong and trapped him in the antimatter universe. Now he wants to return, but he needs a matter counterpart to take his place, and he wants the Doctor.

Driven mad by his isolation and physically corroded to the point where only his will survives inside his armor, he threatens to destroy the universe, but he is tricked into picking up the Second Doctor's recorder -- the only thing not converted to antimatter when they travelled through the black hole -- and is destroyed.

As a reward for saving the universe, The Doctor's exile is lifted and he's able to use his TARDIS normally once more.

!! Tropes

* AGodAmI: Omega
* AndIMustScream: Omega's body has been disintegrated, but he is still alive and conscious. He can't die as long as he believes he's still alive. And he's been in solitude for a few centuries at least.
* {{Antimatter}}: A whole world made of it. And everything transported into it is changed to antimatter too. Except if it's protected by a force field, of course.
* ArbitrarySkepticism: The Brig is rather accepting of the whole anti-matter monsters and black holes situation (he's dealt with weirder, arguably). But he immediately dismisses the idea of two Doctors existing at the same time (he thinks Three must have changed back somehow), and insists the TARDIS interior must be an optical illusion.
* ArtisticLicenseMilitary: British Army officers should not salute civilians. However, given that the Brigadier thought the Doctors were about to do a HeroicSacrifice to save the entire universe, he probably felt bending the rules was justified.
* BattleInTheCenterOfTheMind: The Third Doctor challenges Omega to one of these... and loses, badly. The only reason he doesn't die is because the Second Doctor talks Omega out of it.
* BBCQuarry: The antimatter world, of course.
* BigBad: Omega.
* BigNo: Omega pulls this one off in a disturbingly serious way. His genuinely heartbreaking wail is immediately followed by spoonfuls of {{Narm}}, though.
* BorrowedCatchphrase: Even before the Second Doctor appears, his catchphrase does.
-->'''Third Doctor:''' When I say run, run!
* BrokenPedestal: Omega was the Doctor's childhood hero. It hurt to discover that he had gone nuts and become obsessed with destroying his own race, after having helped them progress so far.
* TheCameo: Gallifrey (although it's not named yet) and a few Time Lords show up for a couple of scenes.
* ChekhovsGun: The Second Doctor's recorder.
* DeadpanSnarker: Two to Three, Three right back at Two, One to Two and Three, Two to the Brig, and the Brig at ''everybody''.
* DramaticUnmask: When Omega reveals his true face to himself and to the Doctors.
* DudeWheresMyReward: Omega is not happy at being forgotten in spite of all of his achievements.
* EmpathicEnvironment: Every time Omega gets annoyed, his fortress rumbles, shaking visibly as the anger increases. Justified because the fortress, and indeed the entire environment within the black hole, is shaped by Omega's mind.
* EvilIsHammy: Omega, so much. To quote WebSeries/SFDebris:
-->This is the kind of performance where Creator/BrianBlessed tells you, 'Can you tone it down a notch?'
* ExactWords: The Second and Third Doctors pledge that they will not attempt to leave Omega's realm before Omega himself. Omega assumes this means they'll stay with him forever. It doesn't.
* FalseReassurance: The Third Doctor says to Omega, "We will not leave here before you do." Omega assumes this means they will stay there with him. It doesn't.
* FutureMeScaresMe: Or rather Future Me Disappoints Me. Also inverted, since in this case Future Me Isn't Exactly Impressed With Me Either.
** And, when there are two Future Mes, ''I'' scare ''them''.
*** And now you can watch it in [[https://www.youtube.com/watch?v=AV4fAwn0N_Mthe ERB format]]!
* IChooseToStay: After spending his last three seasons, trying to get his TARDIS working again and off Earth, the Third Doctor gets his wish, and then decides to stay on Earth and work with UNIT. His successor will not share the same sentiments.
* IHatePastMe: Not so much "hate" as "find incredibly annoying."
* LargeHam: '''Omega.''' EvilIsHammy indeed.
** Everybody, ''everybody'' gets at least one taste of pork products and/or scenery during this serial (for instance, ask TheBrigadier his opinion on the Second Doctor's recorder...). That said, '''Omega'''. It's a wonder they were able to ''find'' any more ham for anyone else once Omega had gotten started.
* LoadBearingBoss: Omega's will is the only thing keeping the antimatter world together. And Omega himself, for that matter.
* MortonsFork: Omega can only escape from his realm by relinquishing control of the Singularity he uses to create the realm. Unfortunately, the very moment he relinquishes control of the Singularity, everything falls apart -- preventing him from escaping.
* MyFutureSelfAndMe: An especially funny case, as the title characters cannot stand each other. Two and Three bicker constantly, and One gets a wonderful dig at them both (see page quote).
* NoFaceUnderTheMask: What is revealed when Omega's mask is removed. It turns out his body was consumed by antimatter aeons ago, and his willpower (and hatred) is the only thing holding him together.
* NoIndoorVoice: Omega is one of the hammiest ''Series/DoctorWho'' villains, and that's saying something.
* NoOntologicalInertia: When Omega is destroyed, both Doctors are returned to the TARDIS and the TARDIS herself is sent back to UNIT headquarters.
* TheNthDoctor
* ObfuscatingStupidity: At one point, the Second Doctor rambles to Omega about his lost recorder, prompting (yet another) tantrum on Omega's part. The Third Doctor reprimands him, only for the Second Doctor to reveal he's just been testing Omega's self-control to find a weakness.
* OmnicidalManiac: Omega could give Davros a run for his money. See VillainousBreakdown.
* OtherMeAnnoysMe: Two and Three have this attitude with each other.
* PercussiveMaintenance: Radio not working? Smack it on the TARDIS console. Voila!
* PortalCut: A green blob teleports the Doctor and part of the building he's in through a black hole, and later the rest of the building. The two parts of the building arrive in different locations. At the end, when everything is sent back to "where it came from", the two parts of the building are re-assembled, apparently without any permanent damage.
* PuffOfLogic: Subverted. This is essentially what will happen to Omega if his will does not dictate that he exists, but Omega's will proves itself too unshakable for him to just disappear.
* PunctuatedForEmphasis: '''Omega's! Entire! Mental! Breakdown!'''
* TheRival: Doctors Two and Three take an immediate dislike to each other, and begin sniping at each other from the moment they meet themselves. Creator/PatrickTroughton and Creator/JonPertwee, in RealLife, loved the effect so much that they decided to carry on the mock bickering, in character and out of character, Jack Benny and Fred Allen-style, in public for the rest of their careers. (In private, they actually became quite good friends).
* RealLifeWritesThePlot: Creator/WilliamHartnell was ill and getting on in years (in fact, this serial was the last time he acted before his death), which is why the First Doctor appears only on a viewscreen.
* RebuiltSet: Another new set to replace the one damaged in "[[Recap/DoctorWhoS9E5TheTimeMonster The Time Monster]]" and commemorate the 10th. Typically, the Second Doctor doesn't like it.
* TheScream: Omega lets out a rather convincing primal wail when he discovers that there's literally nothing left of him but his mind and some dust, animated by willpower alone.
* SealedEvilInACan: Omega.
* ShoutOut: [[Music/TheBeatles "And we are all together, koo koo kachoo?"]]
* SpecialEffectsEvolution: The "organism" is a video effect that, a few years previously, might have been achieved through more practical means.
* [[SubvertedCatchphrase Subverted]] SharePhrase: The "BiggerOnTheInside" line.
-->'''Third Doctor:''' Well, Sergeant? Aren't ''you'' going to say "It's bigger on the inside than it is on the outside"? Everybody else does.\\
'''Sgt. Benton:''' Well, it's... pretty obvious, isn't it?
* SuicidalCosmicTemperTantrum: On learning that he can never leave his antimatter realm, Omega suffers a breakdown and starts vowing to destroy every living thing in the universe.
* TakeThat: The Second Doctor decides that they need to confuse the anti-matter monster with "mindless noise," then wonders if there's a television handy.
** Could also count as a TakeThatMe, since this ''is'' a television series.
* ThrowItIn: Nicholas Courtney's line about Cromer was improvised.
* UnfazedEveryman: Sergeant Benton, as always. Gel monsters? The previous version of the Doctor turning up? The TARDIS being BiggerOnTheInside? He's SeenItAll.
* UnspokenPlanGuarantee: The three Doctors discuss their plan in front of everybody... with a psychic link. Of course it works perfectly.
* UnrealisticBlackHole: There's an entire world of antimatter inside it. And you can just walk up right to the singularity without ill effects. And afterwards, you can walk away from it again.
* TheUnreveal: ''Literally.'' The Second and Third Doctors try to remove Omega's mask and find there is absolutely nothing left of him underneath. Then Omega lifts the helmet off his head and sees the awful result of his time in the black hole... and he goes to pieces with grief and rage.
* VillainousBreakdown: He's not exactly the definition of stability to begin with, but Omega goes completely off the deep end when he finds the aforementioned existence failure. "If I exist only by my will... then my will is to DESTROY, and ALL THINGS shall be destroyed! AAAALL THINGS! ALLLLL THIIIINGS!!!" (Cue second anguished wail.)
* WaxingLyrical:
--> '''Third Doctor''': "I am he and he is me."
--> '''Jo''': "And we are all together, goo-goo-kachoo?"
--> '''Three''': "What?"
--> '''Jo''': "It's a song by the Beatles."
--> '''Two''': "Oh, really?" *Takes out his recorder* "How does it go?"
* WhamEpisode: This brought back the two previous actors who had played the Doctor, a previously unprecedented event, but at the end the format of the series changed as the Doctor's exile to Earth was lifted.
* WhichMe: The Doctors use "me" to refer to their other self, as well as "he".
* WholePlotReference: To ''Film/TheWizardOfOz''.
* WroteTheBook: According to the Doctor, his people invented black holes.
* YourMindMakesItReal: Omega is essentially the god of an antimatter world he's imprisoned in within a black hole. Despite having been destroyed by the singularity's energy, he still exists because of his belief and desire for himself to still be alive.