The one where the Doctor tries to murder his companion.
But more importantly, it's the one with... the coat.
The story where Colin Baker made his explosive debut as the Sixth Doctor, ratcheting wildly from one emotion to another, showing the range of Colin's acting talent in a very upfront manner.
The Doctor isn't recovering well from his regeneration, suffering mood swings, arrogance, bad temper, and terrible dress sense. He suddenly decides Peri is evil and tries to kill her, then one mood swing later is full of remorse and declares his intention to find a deserted asteroid and become a hermit. Peri is not much impressed, particularly since he seems to have decided she has to go and be a hermit too.
As luck would have it, however, the deserted asteroid is also a stopping-off point for a group of kidnappers who have just abducted a pair of identical twin geniuses to assist with a sinister plot. It isn't long before the Doctor's rediscovering his enthusiasm for saving the universe from evil telepathic giant slugs.
This story was pinned onto the end of Season 21 when the idea of introducing viewers to a brand-new Doctor right off the bat instead of making them wait for the next season had merit. However, the end result was very divisive, to say the least: suddenly, the kind and noble Doctor was radically redefined into the polar opposite, a spiky and unpredictable fellow. Regardless of what one thinks of this story (and we cannot stress this enough), it certainly left a mark on viewers.
- Artistic License Astronomy: This story butchers basic astronomic facts so badly — specifically, when the Doctor implies that planets have to be ordered from largest-to-smallest, and that small planets can't be placed near the sun because they'd instantly get sucked into it due to the "gravitational pressure" being too high — that many fans find it easier to believe that the Doctor's scientific knowledge is still messed up from his regeneration, and that Azmael's just going along with him to avoid being strangled again.
- Big Bad: Mestor.
- Bird People: The Jacondans look distinctly avian, with a helping of Big Ol' Eyebrows and mustaches.
- Broken Pedestal: Edgeworth/Azmael, due to his willingness to kidnap children and do other nasty things in order to rid his world of the Gastropods.
- Continuity Nod:
- The Doctor says, "Brave heart, Tegan." He is addressing Peri at the time, who is confused by the injunction.
- Seen in the TARDIS wardrobe are the Second Doctor's trousers, suspenders and coat; the Third Doctor's velvet jacket and checked cape; and Tegan's coat and shirt
- The Doctor wants to take Peri to the Eye of Orion, but he has trouble remembering the co-ordinates.
- The Doctor paraphrases Sarah in "The Hand of Fear" when he says "I don't know if I'm coming or gone or even been"
- Contrived Coincidence: This deserted asteroid suddenly has an awful lot of people on it, doesn't it?
- Creepy Twins: Romulus and Remus aren't evil, but they are spooky mathematical geniuses.
- Deconstruction: If this serial aired today, people would interpret it as a high-profile trolling effort. The Doctor regenerates back into William Hartnell, undoing all of his character development thus far, and what's more, the new costume is eye-searingly ugly? By all indications, this was not John Nathan-Turner's intention; Colin Baker was interested in returning to a darker, less trustworthy Doctor, and Nathan-Turner cast someone who was the polar opposite of Peter Davison. It's hard to explain the outfit, though... except as a deliberate subversion of the hallowed regeneration makeover.
- Six and Peri Brown are assuredly the most controversial portrayal of the Doctor-Companion relationship yet, with the Doctor threatening to abduct Peri against her will and make her into his au pair.
- Dirty Coward: The Doctor, of all people. He does a Security Cling to Peri on facing his first Cliffhanger. He gets better though.
- Does This Remind You of Anything?: SF Debris and El Sandifer noted that, even beyond the obvious strangling, the Doctor's treatment of Peri in this story and the way she responds to it is uncomfortably similar to an abusive relationship. Which is often cited as yet another reason why this story and the Sixth Doctor were and are far from popular.
- Double-Meaning Title: Anyone who has watched it will think of Romulus and Remus when hearing the title, but anyone who knows it as "the first Sixth Doctor story" will think of regeneration and his mood swings. Of course, that sentence doesn't apply to most people - any story with Peri in it is Best Known for the Fanservice. (By the way, there's nothing in it that can really be called a dilemma).
- Dull Surprise: Romulus and Remus. The actors were picked purely for the fact that they were identical twins and it shows.
- Elmuh Fudd Syndwome: The twins both have this... which wouldn't be such a problem if their names didn't both start with "R".
- Establishing Character Moment:
- The Sixth Doctor strangling Peri makes it clear how unstable this regeneration is starting off. Fortunately, the Doctor gets better.
- Mestor has one when he sentences someone to death by embolism for the first time.
- Expy: Mestor is basically a low-budget Jabba the Hutt.
- Family-Unfriendly Violence: The Sixth Doctor, in a bout of post-regeneration psychosis, graphically strangles Peri nearly to death.
- Grand Theft Me: One of Mestor's powers.
- Heel Realization: In a staggering display of paranoia and something he wouldn't normally be capable of, the Doctor strangles Peri due to regeneration sickness. She would have died if she hadn't managed to shove a mirror near his face; he backs away from his reflection, cringing and hiding his face, his sanity briefly restored soon after.
- Heroic Sacrifice: Azmael deliberately triggers a regeneration at the story's end in order to destroy Mestor's consciousness. But since he doesn't have any actual regenerations left, doing so kills him in the process.
- Hypocritical Humor: The Doctor calls out Peri's fashion when redressing, even though his fashion taste is just as bad.
- I Hate Past Me: As usual, the Doctor doesn't think much of his former incarnation.[The Doctor is checking his new appearance in a mirror]
Doctor: Ah. A noble brow. Clear gaze. At least it will be, given a few hours sleep. A firm mouth. A face beaming with a vast intelligence. My dear child, what on Earth are you complaining about? It's the most extraordinary improvement.
Peri: On what?!
Doctor: My last incarnation... Oh, I was never happy with that one.
Peri: Why ever not?
Doctor: It had a sort of feckless "charm", which simply wasn't me!
- Insufferable Genius: Imagine if there were two Wesley Crushers, and you've pretty much got Romulus and Remus.
- And if you shove them into one body you'd get the Sixth Doctor!
- Kill the Host Body: Another Time Lord working for Mestor is possessed by it. Helpless, the Time Lord dies because he was out of regenerations, killing himself and the Big Bad.
- Knight Errant: The Doctor describes himself as one:I'm a knight errant, not an errant fool!
- Large Ham: Colin Baker as the post-regeneration Sixth Doctor is something you need to see to believe.
- Laughing Mad: The Doctor's regeneration trauma runs the gamut of emotions, from "happy drunk" to "raving paranoia" and everything in between. The wardrobe change is interrupted by a bout of existential angst."Nothing but the... urk!... grinding engines of the universe! The... crushing boredom of eternity! HAAAAAHahahahAHAhahahaA!"
- Leaning on the Fourth Wall: The Doctor's speech to Peri near the end is no doubt meant for the audience, as well as her. The Doctor even makes a few good points, shame that didn't save him in the end...Doctor: And I suggest Peri that you wait a little before criticizing my new persona. You may well find it isn't quite as disagreeable as you think.
- Mood-Swinger: The Doctor's moods are completely out of control in this story, as a result of his regeneration.
- My God, What Have I Done?: The Doctor regains his senses just in time to stop his attempt to kill Peri.
- The Nth Doctor: Colin Baker makes his debut as the Doctor.
- Our Graphics Will Suck in the Future: Perhaps the best example is the symphony in higher mathematics which is composed of large pixels.
- Out of Continues: Azmael is on his thirteenth and final incarnation, and dies for good by forcing a regeneration to kill Mestor, who was possessing him at the time.
- Planetary Parasite: This story features the Gastropods, a race of nearly indestructible creatures who devastated entire planets, but whose eggs couldn't hatch unless seared by a supernova first, limiting their spread.
- Pretender Diss: The Doctor gives a brilliant one to Mestor:In my time, I've been threatened by experts and I don't rate you very highly at all.
- Resurrection Sickness: The Sixth Doctor becomes dangerously psychotic and suffers from violent mood swings, first convincing himself that his companion is a spy and trying to strangle her, then declaring that he needs to become a hermit for everyone's safety when he realizes what he almost did.
- Shout-Out: The Doctor quotes from the epic poem "Excelsior." Also, Mestor is a gastropod version of Jabba the Hutt.
- Single-Minded Twins: Romulus and Remus
- Space Clothes
- Taking You with Me: Mestor possesses Azmael, and is defeated when the latter forces a regeneration despite being on his final incarnation. This ultimately kills the both of them.
- Teleporters and Transporters
- Theme Twin Naming: Romulus and Remus.
- 10-Minute Retirement: The Doctor's short-lived career as a hermit.
- Too Dumb to Live: Had Mestor just taken over the Doctor at the end of the story like he claimed he could, he would have won. Instead, he screws around and decides to possess Azmael, a more experienced Time Lord who isn't in the throes of post-regenerative trauma, which leads directly to his defeat.
- We Used to Be Friends: Peri's dismay at what the Doctor has become sums it up:Peri: You were almost young! I really liked you! And you were sweet, and—Doctor: Sweet? Effete! Sweet? Sweet? Sweet? Huh, that says it all!
- The Doctor has a similar moment with Azmael later on.
- What the Hell, Hero?: Peri does not take the Doctor's attempt at strangling her well, not to mention all his mood swings and unpredictable behaviour.
- You Say Tomato: A Running Gag in this story is the different ways in which "Lieutenant" is pronounced, with Peri saying "Loo-ten-ant" (the American pronunciation) and the Doctor and Lang saying "Leff-ten-ant" (the British pronunciation).