The one where the Doctor sets fire to everything and John Nathan-Turner sets fire to the Sonic Screwdriver.
The Doctor lands the TARDIS at exactly the right spot to drop Tegan off at her job, and even has her there a bit early... 315 years early to be exact.
It's 1666, and they're in a rather deserted bit of English countryside. There they meet lovable rogue Richard Mace, an actor-turned-highwayman with an interesting grasp of situational ethics (breaking and entering: bad; stealing: fine), but fortunately the Doctor and company are around to teach him their own superior ethics (breaking and entering: fine; stealing: bad).
In walks the glammest android ever seen in Doctor Who, and laser blasts start firing. Tegan and Adric are taken away for interrogation. The Doctor, Nyssa, and—reluctantly—Richard explore the woods and discover... a shipping container. That is, it looks like a shipping container, but the soundtrack has a synthgasm when Richard points it out, so it's probably something important. Like a spaceship!
Which it is. Doctor, Nyssa, and Richard investigate, and hole up inside to fend off a hilariously futile attack by guys with axes and arrows. They blow the escape hatch and... escape. Nyssa is sent back to the TARDIS to build a remote android jamming device out of spare parts. Which she does. Because she is awesome. Not that she gets any thanks—or even acknowledgment—from the Doctor for her MacGyvering, because the Doctor's a bit of a dick in this story.
The survivor is a Terileptil fugitive. He interrogates Tegan and Adric about the Doctor. Meanwhile, the Doctor and the others find the Terileptil's ship near the manor. They plan how to deal with the android: A sonic booster set up in the TARDIS might just deal with it. As they leave the ship, a group of villagers, all wearing the same device Mace found, approach them. They demand the Doctor come with them. When he refuses, they attack. The three run back into the ship, now under siege by the villagers. The Doctor blasts open the rear hatch of the ship and the group escapes into the forest to find the TARDIS. The controlled villagers follow them at a distance.
Back in the manor, Tegan and Adric have been placed in a locked room. Nyssa heads back to the TARDIS to work on the sonic booster. The Doctor and Mace go to take a horse from a nearby mill to make their way back to the manor. Tegan and Adric escape from the room and go into the manor proper. Adric jumps out a window before Tegan is recaptured by the android. Just before leaving the mill, the Doctor and Mace are confronted by real villagers and are about to be killed for being "plague carriers".
Yet the Terileptil still needs the Doctor. He sends his controlled villagers in to stop them. The villagers throw the Doctor and Mace into a room in the mill. At the manor, the Terileptil has placed one of the bracelets on Tegan. Back at the TARDIS, Adric arrives and assists Nyssa in setting up the sonic booster. The Doctor disables two of the bracelets and the Terileptil sends the android to retrieve them.
Minutes later, the android, in the guise of the Grim Reaper, bursts into the mill, frightens off the villagers and takes the Doctor and Mace back to the manor. They find Tegan under the bracelet's control. The Doctor encounters the Terileptil and his offer to take him away from Earth fails. The Terileptil plans to kill everyone on Earth and take over the planet. Mace is also equipped with a bracelet and the Doctor is thrown in a room where the Terileptil incinerates his sonic screwdriver.
It would be fourteen years until we see the sonic screwdriver again.
The Terileptil brings in a cage with a rat and explains his plan: he will use genetically enhanced plague carried on the rats to devastate the population. The Terileptil leaves the room and the controlled Tegan prepares to open the cage.
The Doctor disables the bracelets and stop both of them. The Terileptil leaves for his base in the nearby city and sends the android to take control of the TARDIS. The Doctor, Tegan and Mace escape from the room and search the Terileptil's lab. It is empty. Mace tells the Doctor that the nearby city the Terileptil referred to is London. The android arrives at the TARDIS but is dealt with by the sonic booster Nyssa finished. Adric and Nyssa move the TARDIS to meet the Doctor and the others at the manor.
Using the TARDIS scanner, the Doctor locates the Terileptil in London. The TARDIS rematerialises there and the five enter the building. With the Terileptil leader are two other Terileptils who get the jump on the Doctor and Mace. They stop them, but one of the Terileptil's weapons overloads and detonates. The explosion destroys the building and starts a raging fire. Mace stays behind to fight the blaze as the Doctor, Tegan, and Nyssa leave in the TARDIS.
The fire is at Pudding Lane, where the Great Fire of London started. Which makes it the second time the Doctor accidentally caused one of the great fires of history.
This serial marks the final appearance and the destruction of the sonic screwdriver in the classic series, as producer John Nathan-Turner claimed it was too much of a convenience for the Doctor, much like K9 was when he was around. The screwdriver wouldn't return onscreen until the TV Movie in 1996. This is also the Doctor Who debut of Eric Saward, who had also just become the series' script editor. (Though since the season was shot Out of Order, he was credited onscreen as early as "Castrovalva", shot later.)
- Alas, Poor Villain: Invoked; Nyssa is upset by the Terileptil android's destruction because it was a slave.
- Alternate Character Interpretation: Invoked Adric's usually insufferable behaviour is revealed to be due to intense insecurity.
- Batman Grabs a Gun: The Doctor seems quite comfortable around guns in this story.
- Been There, Shaped History: The Doctor inadvertently caused The Great Fire of London.
- Bigger on the Inside: Subverted Not the TARDIS — the Terileptil ship, which proves bigger than it looks from the outside. Because the crash impact caused it to partially bury itself in the ground.
- The Black Death: The TARDIS arrives in a village outside of London during the time of the Black Death. The Terileptils plan to use a genetically modified version of the bubonic plague to wipe out humanity.
- Brandishment Bluff: Mace tries to scare off the brainwashed villagers with his empty pistols, but the Doctor informs him it won't work.
- Brown Note: The Terileptil android is destroyed by sound.
- Can't Argue with Elves: The Doctor rolls his eyes at the silly humans and their foibles. Twice. In fact, the Doctor's kind of a dick in this story, which is such a change from Five's usual befuddled niceness that it is wonderful to behold.
- Captain Obvious:Mace: What do we say if the door is opened?Adric: ...hello?Tegan: *eye roll*
- Cargo Ship: "I feel like you've just killed a very old friend of mine."
- Continuity Nod:
- Tegan assumes the Terileptil's interest in the TARDIS means that, like Monarch ("Four to Doomsday"), he wants to "ride in it".
- Whilst in the TARDIS prior to landing, the Doctor rebukes Adric for interfering with the TSS and Tegan talks to Nyssa about her recent possession by the Mara on Deva Loka ("Kinda").
- When the Doctor is about to be beheaded by the scytheman, he groans, "Oh no, not again." He is alluding to the events in "Four to Doomsday", in which he was nearly beheaded by Monarch's androids. In fact, this was a Throw It In! moment as Davison pointed out that the cliffhanger had been used recently and suggested the Lampshade Hanging.
- The Fourth Doctor previously indicated that he was wrongly accused of having started the Great Fire. ("Pyramids of Mars")
- Comet of Doom: The Terileptils' ship is mistaken for a comet and taken as a harbinger of doom by the locals.
- Cowardly Lion: Mace is braver than he thinks he is.
- Dead Star Walking: John Savident was promoted in the run-up to this story as its main guest star. His character gets killed minutes into the first episode (he's the owner of the manor house the Terileptils take over) and never even meets the regular cast.
- Distressed Dude: This is the third time the Doctor's been captured this season—he gets handcuffed too!
- Dual Wielding: Both the nobleman at the beginning of the story and Richard Mace dual-wield flintlock pistols.
- Expy: Eric Saward, who wrote this story, had featured a very similar character named Richard Mace in some radio plays he wrote in the 1970s. Those were set in the nineteenth century, however, so this probably isn't actually the same person.
- The Grim Reaper: The Terileptils disguise their robot as the Grim Reaper to terrorize the local villagers.
- The Highwayman: Richard Mace allows Tegan to imply he's this (though he prefers "gentleman of the road"). Though whether he is truthfully is up for debate.
- Historical In-Joke: The final shot of the serial is a flaming sign reading "Pudding Lane". Pudding Lane is the site where the Great Fire of London began in 1666.
- "I Know You Are in There Somewhere" Fight: Part 3 cliffhanger
- Inspired by : The initial idea for this story was suggested to Saward by a former girlfriend who had recently read about the plague and the fire.
- In the Hood:
- An alien traveling by cart through Restoration England adopts this as a Paper-Thin Disguise that completely fails to cover his reptilian snout.
- The robot also does this, and throws on a skull mask so the superstitious peasants will think it is literally Death itself.
- Kill It with Fire: How the Terileptil leader dies. And you get to see the horrid sight of his face melting to boot.
- Kneel Before Zod: Once again, the Doctor is forced to kneel so he can be beheaded.
- Lovable Coward: Mace proves himself in the end, though, despite his cowardice.
- Lovable Rogue: Richard Mace.
- Mark of Shame: The Terileptil leader has face markings (which double as a nasty disfigurement) that mean if he goes back to his home planet he'll be killed. It's never specified if this was intentionally done by the authorities, or merely the result of being sent to the uniquely dangerous prison/mine. Other criminal Tereleptils in the story without speaking roles did not have similar scars.
- Mind-Control Device: The Terileptil puts bracelets on humans to control their minds. He doesn't bother with The Doctor; he knows The Doctor would be able to resist it.
- No Name Given: The Terileptil is referred to by its race.
- Off with His Head!: The villagers attempt to decapitate the Doctor with a scythe.
- Oh, No... Not Again!: The Doctor's reaction to his imminent decapitation by the villagers.
- Paper-Thin Disguise: The Terileptil hides himself under a Black Cloak that completely fails to cover his reptilian snout.
- People in Rubber Suits: The Terileptil Leader is notable in that it's the first rubber-suit monster to feature animatronics inside the head, which allowed its gills to move and eyes to blink.
- Percussive Maintenance: How Adric gets the TARDIS working properly.
- The Plague: It's already going on, but the Terileptil plans to supercharge it to wipe out humanity.
- Proud Warrior Race Guy: The Terileptils.
- Refusal of the Call: The Doctor offers Mace a place on the TARDIS, but he declines.
- Reptiles Are Abhorrent: The Terileptils. At least their leader is well-spoken.
- Shoot Out the Lock: The Doctor is at one point required to shoot the lock out of a door with a single-shot musket. He fires to no apparent effect, prompting the person he's trapped in the cell with to whine about how he's wasted their only shot and clearly missed the lock. The Doctor then smiles smugly and pushes the door open.
- Shut Up, Kirk!: The Terileptil gets a pretty nice retort to the Doctor's request for diplomacy.Doctor: All this carnage isn't necessary.
Terileptil: It's survival, Doctor. Just as these primates kill lesser species to protect themselves, so I kill them. [turns to leave]
Doctor: That's hardly an argument!
Terileptil: [angrily] It's not supposed to be argument! It's a statement!
- Sinister Scythe: The Doctor and Richard Mace are nearly decapitated by a peasant with a scythe in the belief that they're carrying the plague. Then the android disguised as the Grim Reaper takes the scythe off the peasant—naturally they all run for their lives at the sight.
- Time-Travellers Are Spies: Averted; as strangers in the area they're nearly executed for being plague carriers instead.
- Weapon for Intimidation: Richard Mace attempts to threaten the villagers with a pair of unloaded flintlock pistols. The Doctor points out that the villagers are being mind-controlled and are therefore immune to intimidation.