The one with killer pixels and the Doctor arguing with himself.
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 Like an Old Married Couple 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.
- A God Am I: Omega
- And I Must Scream: 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.
- Arbitrary Skepticism: 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.
- Artistic License – Military: British Army officers should not salute civilians. However, given that the Brigadier thought the Doctors were about to do a Heroic Sacrifice to save the entire universe, he probably felt bending the rules was justified.
- Battle in the Center of the Mind: 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.
- BBC Quarry: The antimatter world, of course.
- Big Bad: Omega.
- Big "NO!": Omega pulls this one off in a disturbingly serious way. His genuinely heartbreaking wail is immediately followed by spoonfuls of Narm, though.
- Borrowed Catchphrase: Even before the Second Doctor appears, his catchphrase does.Third Doctor: When I say run, run!
- Broken Pedestal: 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.
- The Cameo: Gallifrey (although it's not named yet) and a few Time Lords show up for a couple of scenes.
- Chekhov's Gun:
- The Second Doctor's recorder, which he makes a big fuss about having lost, turns out to be just the thing they need to save the day at the end.
- When the Doctor, Jo, and Dr Tyler are first brought to Omega's stronghold, the Doctor does a conjuring trick to make a point to Dr Tyler, then discards the bouquet of flowers he conjured. Later, Jo and Dr Tyler are trying to escape, and get lost in the maze of passages, until Jo finds the flowers on the floor and is able to work back from there to the entrance.
- Deadpan Snarker: Two to Three, Three right back at Two, One to Two and Three, Two to the Brig, and the Brig at everybody.
- Dramatic Unmask: When Omega reveals his true face to himself and to the Doctors.
- Dude, Where's My Reward?: Omega is not happy at being forgotten in spite of all of his achievements.
- Evil Is Hammy: Omega, so much. To quote SF Debris:This is the kind of performance where BRIAN BLESSED tells you, 'Can you tone it down a notch?'
- Exact Words: 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.
- False Reassurance: 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.
- Fisher King: 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.
- Foreshadowing: The Doctor's line that compares being attacked by antimatter to "being punched on the nose by the invisible man" is, notoriously, nonsensical as science, but does serve the purpose of foreshadowing the big reveal about what's under Omega's mask.
- Future Me Scares Me: 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 ERB format!
- And, when there are two Future Mes, I scare them.
- Heads or Tails?: When the Second and Third Doctors are deciding who should risk crossing the "time bridge", the Second Doctor suggests this method, then flips a coin and announces that the Third Doctor has lost. Later, when they're deciding who should risk approaching the Singularity, the Second Doctor pulls the coin out again, and the Third Doctor points out that they both know he's just going to make the Third Doctor go first again.
- I Choose to Stay: 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.
- I Hate Past Me: Three doesn't so much "hate" Two as finding him "incredibly annoying." Averted with One, though, for both Two and Three, who treats him as a voice of reason and hold his advice in great esteem.
- Large Ham: Omega. Evil Is Hammy indeed.
- Everybody, everybody gets at least one taste of pork products and/or scenery during this serial (for instance, ask The Brigadier 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.
- Leaning on the Fourth Wall: The monitor screen in Time Lords' control room, which they use to track down the earlier Doctors, can apparently only display monochrome images, so the earlier Doctors first appear on a screen in black-and-white before being inserted into the present-day story in full colour.
- Load-Bearing Boss: Omega's will is the only thing keeping the antimatter world together. And Omega himself, for that matter.
- Morton's Fork: Omega can only escape from his realm by relinquishing control of the Singularity he uses to create the realm. Unfortunately, the very moment he relinquished control of the Singularity, everything would fall apart — preventing him from escaping.
- My Future Self and Me: 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).
- No Face Under the Mask: 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.
- No Indoor Voice: Omega is one of the hammiest Doctor Who villains, and that's saying something.
- No Ontological Inertia: When Omega is destroyed, everything he had brought into his antimatter universe over the course of the story is returned to where it came from, including both Doctors, the TARDIS, and UNIT headquarters.
- The Nth Doctor
- Obfuscating Stupidity: 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.
- Other Me Annoys Me: Two and Three have this attitude with each other.
- Percussive Maintenance: Radio not working? Smack it on the TARDIS console. Voila!
- Portal Cut: 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.
- Puff of Logic: 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.
- Punctuated! For! Emphasis!: Omega's! Entire! Mental! Breakdown!
- The Rival: Doctors Two and Three take an immediate dislike to each other, and begin sniping at each other from the moment they meet themselves.
- Real Life Writes the Plot: William Hartnell 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.
- Rebuilt Set: Another new set to replace the one damaged in "The Time Monster" and commemorate the 10th. Typically, the Second Doctor doesn't like it.
- The Scream: 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.
- Sealed Evil in a Can: Omega.
- Self-Deprecation: The Doctor's plan to keep the antimatter organism from causing more trouble is to "keep it confused, feed it with useless information" — to which he immediately adds that he wonders if there's TV set handy.
- Shout-Out: "And we are all together, koo koo kachoo?"
- Special Effects Evolution: The "organism" is a video effect that, a few years previously, might have been achieved through more practical means.
- Subverted Share Phrase: The "Bigger on the Inside" 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?
- Suicidal Cosmic Temper Tantrum: 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.
- Take That!: 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 Take That Me, since this is a television series.
- Traveling at the Speed of Plot: The sidekicks escape from Omega's stronghold and head back to the Doctor's lab at UNIT HQ in the Doctor's car while the Doctors confront Omega and then escape themselves. The Doctors, on foot, arrive back at the lab only moments after everybody else, despite everybody else having the car and a significant head start.
- Unfazed Everyman: Sergeant Benton, as always. Gel monsters? The previous version of the Doctor turning up? The TARDIS being Bigger on the Inside? He's Seen It All.
- Unspoken Plan Guarantee: The three Doctors discuss their plan in front of everybody... with a psychic link. Of course it works perfectly.
- Unrealistic Black Hole: 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.
- Villainous Breakdown: 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.)
- Waxing Lyrical:Third Doctor: I am he and he is me.
Jo: And we are all together, goo-goo-kachoo?
Jo: It's a song by the Beatles.
Two: Oh, how does it go? [brings his recorder up to his lips]
- Wham Episode: 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.
- Which Me?: The Doctors use "me" to refer to their other self, as well as "he".
- Whole Plot Reference: To The Wizard of Oz.
- Wrote the Book: According to the Doctor, his people invented black holes.
- Your Mind Makes It Real: 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.