In 1980, the TARDIS is dug up from out of the ashes of Pompeii and immediately taken away by UNIT.
Arriving in ancient Pompeii one day before the disaster, the TARDIS is seen vworping in by a frightened slave. To avoid complicated questions, the Seventh Doctor and Mel simply tell him that they're messengers from Isis. This backfires on them tremendously when Mel repeats the lie to someone who's far more likely to question it. Before long, the two are notorious all over town for claiming to come from the foreign Goddess, and Mel attracts the attention of some high priests who'd really like a word with her.
Meanwhile, the Doctor is acting oddly melancholy, and spends more time in the local tavern than out adventuring. When the city's constant earthquakes cause the TARDIS to sink into the ground, he finally tells Mel what's going on: in 1980, when he was in his Fifth incarnation, UNIT told him that the TARDIS had been excavated in Pompeii. He'd refused to even see her and couldn't cope with the idea, so he'd decided to deal with it when the time came. And now, as soon as the TARDIS brought him to Pompeii, he'd realised that this was the end for him — even if he'd find a way to prevent it, him surviving Pompeii would cause a time paradox. Because if he'd be able to retrieve the TARDIS, the TARDIS would never end up being excavated, and the Doctor wouldn't have known that he needed to retrieve the TARDIS in time.
While Mel makes friends and enemies across town (and ends up in jail a few times over), the Doctor gets sidetracked when a local gladiator takes exception to him and challenges him to a fight to the death. With the help of a tavern owner, they eventually decide to Screw Destiny and make their way back to the TARDIS, which had secretly been stolen by a high priestess — the frightened slave's owner. They trick time by staying inside the TARDIS while the lava engulfs Pompeii, and waiting a few days for it to cool down in a nice TARDIS shape all around them. Then they vworp out, vworp back into the hole in 1980, wait to be excavated and disappear as soon as UNIT isn't looking anymore.
- Actual Pacifist: The Doctor. He's unwilling to fight Murranus no matter how much is at stake.
- Alien Lunch: Though the cuisine is normal for its day, but unfortunately for Mel it's not vegetarian-friendly.
- Ancient Rome
- Ancient Tomb: The TARDIS is hidden in one.
- Aristocrats Are Evil: Well, they're complete dicks, anyway.
- Blasphemous Boast: Though no one is really boasting, Isis worship is frowned upon because she's a "foreign god."
- Rocks Of Divine Retribution: In the minds of the superstitious Romans, at least.
- Book-Ends: The adventure starts and ends at the same archaeological dig.
- The Cameo: The UNIT Captain in the 1980s framing sequences is Muriel Frost, who appeared in Doctor Who Magazine comics a few times.
- Cassandra Truth: Mel, and eventually the Doctor, warn virtually everyone they come across. Very, very few believe it.
- Changed My Jumper: Mel's clothing is conspicuous enough to require changing, but the Doctor's apparently isn't. (Mel hangs a lampshade on it, but the Doctor ignores it.)
- Character Development: Mel claims to have never seen the Doctor this sombre and brooding before, and indeed this is chronologically one of the first times the Doctor's later, more grave personality comes to the fore.
- Chekhov's Volcano: Pompeii.
- Compelling Voice: The Doctor talks two people into sleeping, a bit like an old friend of his...
- Despair Event Horizon: When the Doctor realizes he's reached the site of his last flight, he gives up on escape completely. Only after he realizes that the TARDIS can't be buried where he parked it because it's in the wrong part of the city does he perk back up.
- Don't Call Me "Sir": The Doctor is rather uncomfortable with being called "master" by the slave Aglae, probably because of that aforementioned old friend of his.
- Face Death with Dignity: The Doctor is preoccupied with the idea, and whether he can cheat fate again. Murranus and his gladiator compatriots also do this in their arena, deciding that the shame of fleeing would make living unbearable, so they'll take their chances staying where they are.
- "Fawlty Towers" Plot: After Mel casually repeats the Doctor's statement about coming from Isis, the lie spirals completely out of control.
- Fixing the Game: Murranus is using loaded dice to attempt to cheat the Doctor. According to the Doctor this just changes the contest from gambling to dexterity, to see who can toss the dice more skillfully. It's not Murranus.
- Foreseeing My Death: The Doctor believes this to be the case, since his TARDIS was found buried in volcanic ash at the ruins of Pompeii. It causes him to be unusually despondent and fatalistic for much of the story, while Mel refuses to give up.
- Generic Graffiti: Mel thinks this is probably the first appearance of it.
- Gladiator Games: The Doctor is forced to participate by Murranus.
- Hair-Trigger Temper: Gladiators.
- Honor Before Reason/Revenge Before Reason: The Doctor slighted Murranus' honor (in Murranus's mind, anyway) and must die.
- Happiness in Slavery: Well not entirely happy but Tiberus and some of the slaves refuse to leave their mistress.
- Is It Something You Eat?: Inverted. When Mel says she's a vegetarian, the question is "Where is that?"
- Lost Him in a Card Game: The Doctor puts up Mel as stakes in a card game, but wins.
- Not Cheating Unless You Get Caught: The Doctor's theory when playing dice against Murranus, who was also cheating. By extension, it's also how he gets out of the time paradox.
- Oh My Gods!: Well they are in the Roman Empire.
- Prongs of Poseidon: The Doctor is offered a flavour IV in the Gladiator Games.
- Slave to PR: Murranus depends on the good will of the crowd to remain alive when he loses a gladiatorial match. He feels shamed by his defeat at the Doctor's hands (despite the fact that he provoked it in the first place), and will go to any length to kill the Doctor and regain his reputation.
- Slipping a Mickey: Murranus has Valeria offer the Doctor drugged wine so that he can kidnap him and take him to the amphitheater.
- Snowball Lie
- Temporal Paradox: The reason why the Doctor doesn't outright leave; if he had, he wouldn't have known his destiny, so he wouldn't leave outright, so it would start again at the start.
- The Trickster: He's already a Guile Hero, but Seven gets an In-Universe reputation as one here.
- The Queen's Latin: All the Roman characters speak in very old-fashioned and proper English, compared to the Doctor and Mel's more colloquial speech.
- Trapped in the Past: The Doctor knows the TARDIS will be unearthed at Pompeii, leaving him stuck in ancient Rome. Well, or not.
- Tricked Out Time: The Doctor tries this right out of the gate, asking Mel if she'd like to leave as soon as they arrive. Since her decision wouldn't be based on knowledge of the future, there wouldn't be a time paradox and the Doctor could postpone this particular reckoning. Unfortunately, it doesn't work; Mel decides it won't hurt to look around ...
- Once the Doctor is able to break out of the Despair Event Horizon, he comes up with a really complicated plan to weasel out of it. He and Mel get back into the TARDIS, and sit tight for a few days as the lava hardens around them. Then, with a bit of careful piloting, they nip forward to the 1980s without actually moving in space at all. UNIT digs them up, tell the Fifth Doctor... and the Doctor and Mel fly off again as soon as everyone's stopped paying attention.
- What Happened to the Mouse?: Deliberately. The Doctor and Mel never do find out what happened to the people they befriended in this episode, and their fates are unknown to the audience too.
- You Can't Fight Fate: Why the Doctor's in such a sombre mood for this one. Way back in his fifth body, he discovered the TARDIS had been dug up from the ruins of Pompeii and was forced to assume that meant he was dead or trapped in the past. Eventually subverted, as the Seventh Doctor finds a way to avoid that outcome without causing a paradox.