The Doctor and Donna land in Ancient Rome, ready to have more fun than an amphora of monkeys.
Except after some searching, they discover that they've landed in Pompeii, on Volcano Day, approximately 24 hours before Mount Vesuvius erupts and Pompeii's streets get re-paved with lava. Donna immediately requests the Doctor's help to organize a mass evacuation and save everyone, but the Doctor shuts the idea down: he doesn't say "You can't change history, not one line", but he is probably thinking it.
So they go for the other secret Time Lord manoeuvre: running away, much to Donna's frustration. Unfortunately, the TARDIS is missing; while they were walking around, a street merchant seized it (justified; it was parked on his market patch) and sold it to Caecilius, a local marble merchant (played by Peter Capaldi) with a dysfunctional family (a hungover son and an oracle daughter) AND a taste for avant-garde art. It's not the first time the TARDIS has been mistaken for an art installation.
In no particular order: Caecilius' villa is later attacked by a massive magma-man (which is stopped by a bucket of water), and it is revealed that the volcano fumes inhaled by his oracle daughter to boost her visions are slowly turning her into stone. Also, a local prophet claims that there's something on Donna's back. This will be important later. And he says that a planet has apparently gone missing. This will be very important later. Meanwhile, Caecilius has a freaking computer circuit made of stone, so the Doctor decides to stick around a bit longer for the above events.
The Doctor confronts the oracles of the Sybilline Sisterhood (with a Walther P38 water pistol) and finds out why someone ordered a load of marble power-converters.
To his horror, the Doctor finds out that Mount Vesuvius won't erupt if he just leaves; he needs to make it erupt. If Pompeii isn't destroyed, then since the alien menace of the week hasn't also been destroyed, a race of lava golems will turn humans into more golems, boil the ocean and conquer the world. Donna realises for the first time that travelling with the Doctor can be very morally disturbing. They make the volcano erupt, both fully expecting to die, but it turns out the conversion device they used was inside an escape pod. Donna convinces the Doctor to go back and save Caecilius and his family. Because not everyone is an über-depressed near-suicidal Time Lord, and sometimes the Doctor forgets that.
Six months later, Caecilius and his family have their lives back on track, the daughter is finally socialising like a (in our time, anyway) normal teenager, and that wastrel son is making good of himself, studying to be a doctor (not that kind). And their new household gods on the altar, with a box flanked by this man and this woman, look suspiciously familiar...
The casting for this episode turned out to be quite auspicious. Phil Davis ("Lucius") would play the first antagonist in Sherlock (a series run by the same showrunners as Doctor Who); Tracey Childs ("Metella") had previously appeared as Dr. Elizabeth Klein in Big Finish Doctor Who, who would go on to become a regular Big Finish companion; Karen Gillan (Soothsayer scout) would return as Amy Pond, one of the two longest-serving companions of the new series; and Peter Capaldi ("Caecilius") would have a supporting role in Torchwood: Children of Earth and later take the helm of the show as the Twelfth Doctor himself, the episode "The Girl Who Died" featuring a Call-Back to this episode as the reason Twelve has Caecilius' face.
- Accidental Art: Played for Laughs, as Caecilius is sold the TARDIS as a work of modern art. His wife calls it a "great waste of space", not knowing that the TARDIS is Bigger on the Inside. Capaldi then went on to become a later resident of the TARDIS...
- Ancient Rome: Sort of; we'll get there eventually.
- Arc Words: Medusa Cascade, a missing planet, "she is returning", the Shadow Proclamation, and something on Donna's back.
- An Arm and a Leg: The Doctor breaks off Lucius' stone right arm during their confrontation at his house.
- Badass Boast: One is made on behalf of the Doctor by a semi-delirious Evelina, when the apparently genuine psychic abilities of the seers of Pompeii are revealed.Even the name Doctor is false. Your true name burns in the stars, hidden in the cascade of Medusa herself. You are a lord, sir. A Lord of Time.
- Been There, Shaped History: The Doctor is quick to deny that he had anything to do with the Great Fire of Rome. By the end of the episode, he and Donna are personally responsible for the eruption of Mount Vesuvius (as the alternative would be letting the Pyrovile race Take Over the World).
- Big "NO!": Lucius Petrus Dextrus and the High Priestess, when their Evil Plan is foiled. Both do it twice.
- Brick Joke: At the start of the episode, the Doctor says that Latin doesn't have a word for "volcano", and it won't until tomorrow. One day later, while watching Pompeii drown in lava, Caecilius coins the word from the name of the Roman god of fire, Vulcan.
- The Doctor's mention of "Volcano Day" refers to a comment by Jack Harkness in "The Doctor Dances", who mentioned using Pompeii several times to pull cons where he'd sell alien ships or technology, only for the eruption to wipe away the evidence before his mark's realized that he'd actually sold them bits of old junk.
- The Doctor mentioning that he had nothing to do with Rome burning. "...Okay, maybe a little bit."
- Can't Argue with Elves: The Doctor tries this, when arguing that as a Time Lord he's got the say of what should and shouldn't happen. Donna's not having any of it.Donna: What, and you're in charge?
The Doctor: TARDIS, Time Lord, yeah!
Donna: Donna, human, no! I don't need your permission, I'll tell them myself!
- City of Weirdos: The Doctor assures Donna they won't stand out, as ancient Rome is "like Soho, but bigger". It still applies after it turns out they're in Pompeii.
- Climactic Volcano Backdrop: And inside Mount Vesuvius, no less.
- Come with Me If You Want to Live: The Doctor does this at the end for Evelina's family, though he just says "Come with me." This time, Caecilius doesn't argue.
- Continuity Nod:
- Convection Schmonvection: Justified; most of the heat is being taken by the Pyroviles.
- Crazy Awesome: "You fought her off! With a water pistol! I bloody LOVE you!"
- Creator In-Joke: Latin students everywhere stand a chance of recognising Caecilius, Quintus and Metella. They feature in the Cambridge Latin Course, a widely-used Latin textbook series.
- The Cretaceous Is Always Doomed: There's no saving Pompeii. It's a fixed point in history. The possible alternative of a Pyrovile-run Earth doesn't help much.
- Deadpan Snarker: The Doctor, when Donna is about to be sacrificed. Also counts as a Walk-In Chime-In.Sister Spurrina: This prattling voice will cease forever!
The Doctor: Oh, that'll be the day.
- Establishing Character Moment: Donna sharing the burden with the Doctor of having to cause Vesuvius's eruption, and later pleading with him to save just one family. It's not hard to see why the Doctor became such good friends with her.Donna: Just someone. Please. Not the whole town... Just save someone.
- Fainting Seer: Evelina, after telling the Doctor that he is a "Lord of Time".
- Following in Their Rescuer's Footsteps: At the end, Quintus has been inspired by his rescue by the Doctor and Donna to go to Ancient Roman medical school.
- A God Am I: It's a inverted trope here. The new "household gods" of Caecilius' household are the Doctor, Donna and the TARDIS. None of those three believe themselves to be gods no, not even the TARDIS.
- Happily Married: Caecillius and Metella look like a modern stereotype; bickering about household furniture, raising children, he can't find a pin because she's polishing it, and sticking together in tragic times.
- Historical-Domain Character: In reality, Lucius Caecilius Iucundus was a Roman banker who lived in Pompeii at the time of the 62 AD earthquake, during which he most likely died. He's most well known to modern audiences due to being fictionalised by the Cambridge Latin Course, in which he survived the earlier quake to perish during the Vesuvius eruption, seventeen years later.
- Of course, there could just be more than one Caecilius in Pompeii. Also Caecilius' introduces himself as Lobus Caecilius, meaning that he must be a different Caecilius.
- Holy Backlight: When the Doctor comes back to save Evelina's family, light pours out of the TARDIS door behind him.
- I Am Spartacus: Says the Doctor. "And so am I," says Donna. Caecilius, obviously not getting it, first assumes them "Mr. and Mrs. Spartacus", then "brother and sister".
- I'm Mr. [Future Pop Culture Reference]:
- With bonus I Am Spartacus joke included absolutely free.
- 2000 years later, the English language itself still frequently throws Latin into everyday conversation.
- Innocuously Important Episode: While it appears to be your average Monster of the Week/Historical Period of the Week Doctor Who episode, even aside from the standard Foreshadowing and retrospective casting jokes, the events of this episode directly influence the Twelfth Doctor's choice of appearance, most of 6 real-time years later (In-Universe, around 1100).
- Keep It Foreign: The TARDIS's telepathic field translates Latin phrases in Celtic (Welsh today) phrases, and English into Latin.
- Kill It with Water: Or a Walther P38 water pistol.
- Living Lie Detector: Both augurs/soothsayers visibly unnerve the Doctor and Donna by seeing right through their stories and made-up identities and telling them things about them they couldn't have possibly known.Lucius: Is that so? Man from Gallifrey. [...] And you, daughter of... London.
Evelina: Is that your opinion... as a Doctor? [...] And you, you call yourself Noble... [...] You are a lord, sir... a Lord of Time.
- Mass "Oh, Crap!": The Pompeiians, Herculaneans, and Stabiaeans have one once Vesuvius erupts.
- Meaningful Name: Lucius Petrus Dextrus (literally translating to Lucius Stone Right Arm!). These were all deliberate Russell T. Davies was channelling Asterix and asked James Moran to put them in.
- The name "Lucius" is a subtle hint that he's a bad guy.
- Caecilius. His first appearance is him gushing over his new "modern art" item: the TARDIS. When the Doctor and Donna both introduce themselves as "Spartacus", and Caecilius assumes they must be brother and sister, he states they do look a lot alike, at which they emit a puzzled "Really?" in unison. Amusingly, "caecilius" means "the blind one".
- Mistaken for Exhibit: Not only is the TARDIS mistaken for a modern art installation, but an enterprising street trader has sold it to a wealthy marble merchant, kicking off the plot. It's meant to be Played for Laughs.
- Mistaken for Special Guest: Not addressed in the episode, but there's a subtle indication that Donna is seen as someone of high status, when the soothsayers note her true name is "Noble" and that throughout this episode she wears purple, which was seen at the time to indicate wealth and status, even to be an Imperial colour, because of the sheer expense of the dye.
- Noodle Incident:
- Oh, Crap!: The Doctor is initially unimpressed (and slightly amused) by the supposed prophets. Then Evelina calls him a "Doctor" and Lucius addresses him as "Man from Gallifrey", which clearly alarms him.The Doctor: ...What?
- Outrun the Fireball: Or, in this case, the advancing wall of volcanic ash and lava rolling all the way to Pompeii.
- Pity the Kidnapper: The priestesses abduct Donna while the Doctor's back is turned. When he shows up at their temple, neither he or Donna are very concerned about the situation. Note that Donna was about to be killed (mainly for blasphemy, but also for being... well, Donna).
- Potty Emergency: While Donna is unsuccessfully attempting to warn Caecilius of the impending volcanic eruption(him never having heard of a "volcano"), the Doctor seems to get uncomfortable to the point of putting his hands in his pockets, leaning forward, making a "strained" expression, suggesting Donna's "waste of time" is getting to his bladder...
- Prescience Is Predictable: "It must be awful being a prophet, waking up every morning, 'Is it raining? Yes, it is. I said so.' Takes all the fun out of life"; so says the Doctor.
- Prophecy Twist: The Doctor says Pompeii's destruction is "a fixed point" that he can't prevent, even though thousands will die. As it turns out, he has to make Vesuvius erupt to save the world. When the Doctor realizes this, he's understandably stunned, as is Donna when he tells her.The Doctor: ...but that's the choice, Donna: it's Pompeii or the world.
Donna: ...Oh my god...!
- Psychic Powers: The Sibylline Sisterhood have them as a side-effect of the Pyroviles' presence. To be specific, the humans had the powers already, albeit dormant. The Pyroviles activated these powers (the backlash of the sheer force of the eruption, rippling back through time and space, also had something to do with it), though the Doctor mentions a difference between "pyschic" and "seeing the future".
- Punny Name: The producers must have had a lot of fun inserting any Ancient Rome puns they could, like Lucius Petrus Dextrus, Donna asking Evelina if she's been to TK Maxximus, and an obligatory I Am Spartacus joke.
- Running Gag:
- Because of the TARDIS, Donna (and we) hear the Romans' Latin as English, so if you speak to them in Latin, it's translated into a Celtic language. When the Doctor and Quintus are cornered by Lucius Petrus Dextrus and his men, the Doctor mutters, "morituri te salutant" ("those who are about to die salute you") and Lucius Petrus Dextrus says, "Celtic prayers won't help you now."
- Caecilius mistakes the Doctor and Donna for a couple.
- Sadistic Choice: Save Pompeii and let the Pyroviles convert everyone, or save the world and let Pompeii be buried.
- The Punny Name Running Gag is a reference to Asterix.
- To Fawlty Towers, when the Doctor explains away Donna's ignorance of what an augur does with "she's from... Barcelona."
- The scene of Caecilius's family rushing to their positions during the pre-eruption earthquakes could be one to the Admiral Boom scenes in Mary Poppins, with a character shouting "Positions!"
- Caecilius, Metella and Quintus come from Cambridge Latin Course, the most popular Latin textbook in the UK and US (not Evelina, though she was created especially for the episode).
- The Doctor drops a reference to the upcoming 1906 San Francisco earthquake. Caecilius assumes "San Francisco" is the name of a new restaurant in Naples.
- Small Role, Big Impact: While Caecilius and his family only appears in one episode, they have a big enough impact on the Doctor for him to subconsciously model an incarnation on Caecilius' face, hundreds of years later.
- Sistine Steal: The Doctor steps out of his TARDIS to save a doomed family from the title eruption. The TARDIS is unaccountably shining behind him, and then there's a shot of his hand, reaching out for the father's as if he's God and the human is Adam in the Sistine Chapel painting.
- Spared by the Adaptation: Sort of, even though it's not a direct adaptation; see Creator In-Joke and Historical-Domain Character. In the Cambridge Latin Course, Caecilius and most of his family died in the eruption of Vesuvius. However, that man's name was Lucius Caecilius, while Caecilius introduces himself as Lobus Caecilius.
- Spiritual Successor: To "The Myth Makers". The scene in which Caecilius introduces the TARDIS to his wife is even a loving homage to an almost identical dialogue between Paris and Cassandra.
- Taken for Granite: A side-effect of the Pyroviles taking over their human hosts is stone limbs. The Sybilline High Priestess is even farther along, looking like she's completely made of stone, hence her hiding behind a curtain.The Doctor: The people of Pompeii are turning to stone before the volcano erupts.
- Take Over the World: The Pyroviles plan to emulate Rome by taking over the entire known world and likely everything else on the planet.
- Temporal Mutability: Donna asks why saving Pompeii would be different from all the other times the Doctor saves people. The Doctor retorts that some things in time are changeable, some aren't, and the ability to tell one from the other is part of being a Time Lord. Of course, the two of them have to personally make Vesuvius erupt to save the rest of the planet.
- Translator Microbes: Explored when the Doctor tells Donna about the translation field, she wonders what happens if she intentionally speaks Latin. Answer: The Pompeiians don't understand your Celtic.
- Walk-In Chime-In: The Doctor, upon entering the Sybilline temple.
- Watching Troy Burn: The Doctor gives Evelina's family a front row seat to watch Pompeii's funeral pyre, but assures Caecilius that one day, Pompeii will be found again, in the future.
- Weaksauce Weakness: A giant, badass-looking alien warrior made of magma and rock... and a bucket of water takes it down in seconds. The Doctor later uses this to his advantage by arming himself with a water pistol.
- "Where Are They Now?" Epilogue: The family Donna and the Doctor saved reestablish themselves in Rome. Marble business continues, Evelina is wearing a short skirt that's the latest fashion, and her brother is studying to be a doctor.
- What Have We Ear?: The Doctor does this to Quintus to bribe him into taking him to Lucius Petrus Dextrus's house.
- The X of Y: "The Fires of Pompeii".
- You Have Got to Be Kidding Me!: Donna's rather atypical response to almost being turned into a very typical altar sacrifice. Well, almost.
- You Have to Believe Me!: The Doctor tries to discourage Donna from warning people about Vesuvius erupting, saying she'll be dismissed as a mad soothsayer. When it does erupt, she tries to scream to people not to go to the beach (where the ash cloud will still be lethal), but no one listens to her.