The one where the Brig shoots a statue.
The Doctor tries to explain to Jo that there's no such thing as magic while he rigs a remote control gadget for Bessie. He suddenly becomes uncharacteristically alarmed by a planned archaeological dig on a barrow in the village of Devil's End. He races there with Jo in tow, where he discovers that The Vicar, Mr. Magister, is really the Master in a pair of fake glasses (no way!) who is using what looks like black magic rituals to summon the Devil.
In fact, the "devil" is a Sufficiently Advanced Alien called Azal, who actually inspired most of the classic appearance tropes of the Devil — horns, hoofs, shaggy goat legs — and claims to have set the Earth in motion as an experiment. UNIT (reluctantly) teams up with a local white witch, the Master babbles incantations while hanging out with cowled cultists and lighting black candles, and the archaeological dig unleashes a cold field. The Doctor almost dies, but is able to use his Bizarre Alien Biology to withstand extreme cold. His rescuers are rather confused by his two hearts.
The Doctor confers with UNIT by drawing equations on his motor bike's wind shield, and makes it back to the village in Bessie, where he's immediately tied to the maypole by the local Morris dancers. They want to burn him at the stake for being a witch. The local actual witch and UNIT help him out using parlor tricks, and he's able to impress the villagers with Bessie's remote control.
With the Doctor and Jo in the village, and UNIT troops cut off outside by a heat barrier, Azal appears and says that he will either pass on his powers or destroy the Earth as a failed experiment. The Master is hoping to be the recipient of the powers. The Doctor insists that it's not magic, but alien science, and explains to the local witch that even her magic is just invisible science powered by her mind. Azal is swayed by the Doctor's eloquent defence of Earth and offers him the powers instead. The Doctor of course refuses, and Azal angrily decides to kill him. Jo offers herself in the Doctor's place and Azal, unable to comprehend self-sacrifice, suffers a Critical Existence Failure.
Meanwhile, UNIT troops have got past the heat barrier by reversing the polarity, the Brigadier has ordered Five Rounds Rapid at animated gargoyle Bok, and they arrive just in time to apprehend the Master and take him away to await trial for crimes against humanity: attempting to conquer the world, subjugation of the people of Devil's End, and infliction of Morris dancers on an unsuspecting public.
Trope Namer for Five Rounds Rapid, and the source of the famous "reverse the polarity" line. It is one of the few five-part stories in the series' history, and the only one always intended to be that way: Season 6's "The Dominators" began life as a 6-parter but two of its planned instalments were compacted down into one during a contentious scripting process, and the following serial, "The Mind Robber", was expanded from 4 episodes to 5 to make up the difference.
An excellent documentary, "Return to Devil's End", was made in 1996 by Nicholas Briggs and stars most of the original cast.
- Ancient Astronauts: The story reveals the existence of a race of aliens that resemble demons from classical art, and suggests that they were objects of worship for ancient and medieval pagans.
- Arbitrary Scepticism: The Doctor goes to great pains to explain that something that looks and functions exactly like magic is not, in fact, magic. His argument seems to amount to "Because I don't want to call it magic." Also something about Clarke's Third Law.
- Artistic Licence History: Bok is routinely referred to as a gargoyle. Gargoyles were medieval stone carvings on the outsides of churches, usually grotesque, and had a practical function as part of the building's guttering. Bok, while a grotesque, is a statue that sits on a plinth inside the church and therefore not a gargoyle.
- Ash Face: Rare live-action example, when the anti-heat-barrier machine blows up in Osgood's face.
- Attack of the 50-Foot Whatever: When Azal first gets out, he goes for a walk around while thirty feet high. Everyone misses it due to it being the middle of the night, but Yates and Benton see the results from the air the next day.
- Bad Habits: The Master poses as a priest.
- Big Bad: The Master is the one who sets things off with his attempt to gain Azal's powers.
- Bilingual Bonus: The Doctor at one point is dubbed "The Great Wizard Qui-Quae-Quod". In Latin, qui, quae and quod are respectively the masculine, feminine and neuter forms of the pronoun "who".
- Burn the Witch!: The locals try to do this to the Doctor. Ironically the local witch intervenes to stop them (with the help of Benton).
- Butt-Monkey: Osgood repeatedly gets berated and has his competence questioned by both the Doctor and the Brigadier, has to build a device he'd never even considered possible based only off the Doctor's brief description, gets left with an Ash Face when the first attempt at building the machine blows up in his face, and when he does eventually manage to get it working, it only lasts for a few minutes before blowing itself sky-high, nearly taking Osgood with it.
- Campbell Country: The Doctor and UNIT investigate strange goings-on in the quaintly named village of Devil's End, where devil-worshipping villagers led by an evil vicar are attempting to awaken an ancient evil that lies buried beneath the village church, while being opposed by a white witch who is considered the town nutter. While given a (slight) sci-fi bent, all of these elements could have been lifted out of a Hammer Horror film of the period.
- Cassandra Truth: Ms. Hawthorne is on the money about the Master's antics bringing bad things down on Devil's End, but because she's very vocal about her witch qualifications, everyone else (or at least the ones not working for the Master) think she's a kook.
- Chekhov's Boomerang: The remote control unit for Bessie, used to convince the townsfolk that the Doctor is a wizard and to recapture the Master.
- Clark Kenting: The Master wears a pair of thick, Clark Kent-like glasses as Rev. Magister.
- Closed Circle: Somewhat literally until UNIT breaks through.
- Cold Iron: During their first encounter, the Doctor fends Bok off with an iron trowel. It's suggested that this only works because Bok expects it to.
- Collapsing Lair: The church blows up at the end.
- Corpsing: In the long shot just after the Doctor gets caught up in the middle of the Morris dance when they all round on him and begin hitting him with their sticks and bladders, you can see Jon Pertwee is cracking up. (Despite the ludicrous description, this is supposed to be a scary scene.)
- Creator Cameo: Director Christopher Barry voiced an RAF pilot.
- Dance Battler: The Morris dancers use their dance to take the Doctor prisoner. Morris dance is an actual English tradition, and the dancers are the local Morris team, the Headington Quarry Morris Men.
- Dance Party Ending: As the Master is taken away to prison, everyone joins the villagers dancing around the maypole.
- Doing In the Wizard: The Doctor and a career witch argue for several minutes as to whether an effect is magical or scientific. Then the Doctor explains that it works exactly how the witch thought it did, but if you know how and why it works then that's science.
- Evil Cannot Comprehend Good: When Jo throws herself in front of the Doctor, the idea of this actually destroys Azal.
- Evil Is Hammy: Azal; literally every one of his lines is solid shouting.
- Evil Laugh: The Master really hams it up here with aplomb.
- Failed a Spot Check: Jo hides behind the spokes of a wooden wheel while the Master does his thing and tries to sacrifice a chicken. No one sees her.
- A Fête Worse Than Death: The Doctor is captured in a tangle of maypole ribbons, clubbed into unconsciousness by Morris Dancers, and wakes up to ye olde stake/kindling combination.
- Five Rounds Rapid: Trope Namer. Not an entirely straight example, as Captain Yates does call up an anti-tank weapon once it's clear small arms fire isn't doing any good.
- Geometric Magic: A painted tile in the cave knocks out Benton and tears a book to pieces when touched.
- God Guise: Kind of a given for Sufficiently Advanced Aliens. Azal and other Dæmons were the inspiration for many horned pagan gods and Satan.
- Godwin's Law: When the Master pleads for Azal's power so that he may bring order to the world, the Doctor compares him to Adolf Hitler and Genghis Khan.
- Ham-to-Ham Combat: The Master and Azal.
- Harmless Freezing: Zigzagged. The Doctor and the professor leading the dig get frozen at the end of Episode One, which kills the Professor stone dead, but just puts the Doctor out of commission for a few hours (possibly justified given the Doctor's Time Lord physiology, though it's not mentioned onscreen).
- Hollywood Silencer: Benton uses one... but to be fair, maybe UNIT has developed one to work like that.
- Hell Is That Noise: The sound effect used to signify the heat barrier. Not helped by the fact that the distracting sound makes it seem like the characters are stuck in a cartoon blizzard.
- Hellish Copter: One of the cultists chases the Doctor in a helicopter, trying to force him into the lethal heat barrier, and ends up flying into the barrier himself, causing the helicopter to explode.
- Human Sacrifice: The Master plans on doing this to Jo.
- Hypocrite: The Brigadier says he's planning to blast his way through a forcefield. Jo criticizes him for always thinking of blowing things up. The Doctor then berates Jo for not showing the Brigadier due respect - even though he's always saying the exact same thing, and in fact said as much about the Brigadier's plan himself at the beginning of the conversation.
- When talking to each other from across the Heat Barrier, The Brigadier warns The Doctor to keep his distance lest he be flash-incinerated by it. He's standing closer to the barrier than The Doctor is.
- Hypocritical Humour: Probably intended when the Doctor upbraids Jo for mocking the Brigadier in the way that he constantly does, but it's played sufficiently seriously to appear genuinely unpleasant and bullying to many fans.
- I Don't Like the Sound of That Place: Devil's End
- Improbable Aiming Skills: During the "Great Wizard Quiquaequod" scene, Benton shoots out a lamp on the far side of the road and the weathercock on top of the church, through a narrow aperture and with only a handgun (with a silencer attached). In the novelization, Benton has a quiet Oh, Crap! moment when the Doctor calls the weathercock as the next object he will move with his "magic", guessing that the Doctor has assumed he has a rifle instead, and needs two shots to hit it.
- I Need a Freaking Drink: The only abstainee from the dancing at the end is the Brigadier, who decides he'd much rather go to the pub and have a pint.
- Insistent Terminology: The Doctor insist what the Master is doing is "the secret science of the Dæmons" and NOT MAGIC. Everybody else calls it magic because the Doctor fails to clarify why it isn't since there is no difference between the two going by the descriptions in the story and freely admits that the rituals, spells, etc are what make up the secret science having a purpose and are not window dressing.
- Jerkass: Professor Horner, the man leading the dig at Devil's End is a cantankerous old grump. Nobody seems terribly upset when he's turned into a popsicle.
- Jerkass Ball: The Third Doctor spends much of this story being really quite nasty to people who are trying to help him, especially Jo and Osgood. It may be due to the level of the threat posed by Azal (and the Hostility on the Set surely didn't help), but the story is still often used as Exhibit A by fans who dislike him.
- Kill and Replace: Mr. Magister is the new vicar of Devil's End, after the previous, much nicer incumbent, suffered a case of "mysterious causes" in the middle of the night.
- Look Behind You: The version where the villain says they're not going to fall for that old trick and then it turns out there really is something behind them.
- Magic from Technology: The Dæmons powers are handwaved as highly-advanced science.
- Magic Versus Science: A theme throughout the story is whether magic is real. The Doctor insists it isn't and claims there is a rational explanation behind everything. Yet he admits the incantations, rituals, symbols are not for show and all have power and purpose matching the definition of magic given by the local white witch and most real-world definitions. Neither the Doctor or the Master fully understand how it works. Yet the Doctor insists it is the "secret science of the Dæmons" never citing a real difference. In the end (as with most examples of this trope in the show), both views/terms come out as being correct with Dæmon science portrayed as a type of Rules Magic and the Doctor coming across as a close-minded, pompous jerk. Looking at the other tropes in this story reinforces this idea.
- The Master: Duh.
- Meaningful Name; two In-Universe examples:
- The Doctor immediately realizes who the "Reverend Magister" must be as soon as he hears the name: "Magister" is Latin for "Master".
- The name "Quiquaequod" is a mix of Latin conjugations for the word "Who".
- Minion with an F in Evil: The cultist who gets upset when the Master decides to sacrifice Jo. He had an expanded role in the novelization, including a name, a side plot of his own, and a heroic attempt to stand up to the Master, only to be brutally knocked aside.
- Mother Nature, Father Science: The Doctor is contrasted to Miss Hawthorne, a witch. The text seems to suggest that they're similar, however.
- Names to Run Away from Really Fast: Azal, Reverend Magister, Devil's End.
- The Master's hypnotism doesn't work on Ms. Hawthorne.
- Captain Yates tries to stop one of the Master's hypnotized mooks from stealing the helicopter, punching him full in the face; the man barely flinches.
- Ominous Latin Chanting: During the totally not magic ceremonies. Very little of it is genuine Latin; most of it is derived from writing out nursery rhymes and cast members' names backwards.
- Our Gargoyles Rock: Bok.
- Recycled IN SPACE!: Quatermass and the Pit IN WILTSHIRE INSTEAD OF KNIGHTSBRIDGE!
- Reverse the Polarity: Apparently, it's possible to "channel the entire output of the national power complex through one transistor", but there's only one way to do it safely: "Reverse the Polarity."
- Road Sign Reversal: When the Doctor is on his way to Devil's End, a freak wind caused by Azal's, erm, totally-not-magic rotates a road sign so that it's pointing down the wrong road, leading the Doctor off track and preventing him from arriving in time to halt the excavation.
- Satan: Well, sorta.
- Sci-Fi Writers Have No Sense of Scale: In a literal but harmless example, the Doctor's drawing of the heat barrier is apparently meant to be drawn to scale, judging by the (also inconsistent) tick marks he's drawn along the base. But he reiterates that the dome is about ten miles wide and one mile high. In his drawing, the dome's height is clearly at least one-fourth its width.
- Sealed Evil in a Can: Azal was imprisoned inside the Devil's Hump until Professor Horner's excavation unleashed him.
- Secret Circle of Secrets: Azal's followers.
- Shapeshifter Baggage: When Azal changes size, he releases his excess mass as heat, or draws heat out of the environment to create extra mass, so it gets very cold when he grows and very hot when he shrinks.
- Ship Tease: A fair amount between Benton and Ms. Hawthorne.
- Sinister Minister: It's the Master, after all.
- Stock Footage: The helicopter explosion is taken from From Russia with Love. It was previously used in The Enemy of the World.
- Sufficiently Advanced Alien: The Dæmons, apparently responsible for many eras of human advancement.
- Tempting Fate: The Brigadier asks Osgood how he's getting on with the device he's been building from the Doctor's rather confusing instructions. Osgood cheerfully says that he's got the hang of it now, and it will be ready in a few minutes. Part of the device immediately explodes, forcing Osgood to revise his estimate to "half an hour, at least".
- This Is My Name on Foreign: The Great Wizard Qui-Quae-Quod and the Rev. Magister.
- Villain: Exit, Stage Left: Subverted. The Master attempts the sort of escape he did in the other stories this season by stealing Bessie, but the Doctor brings the car back by remote control.
- Villainous Breakdown: A very limited amount of disagreement from the villagers when the Master tries to talk to them into helping him rapidly results in screaming demands for obedience and comparisons of them to dust beneath his feet.
- Watch the Paint Job: The Doctor stops the Brigadier from shooting at the Master because he might damage Bessie.
- You Have Outlived Your Usefulness: This gets pulled on Bert during Azal's final appearance, as he attempts to get to the church to warn the Master of the imminent UNIT attack, only to get vaporized by Bok for his trouble.