[[quoteright:350:http://static.tvtropes.org/pmwiki/pub/images/masque_1844.jpg]]
[[caption-width-right:350:TOUCHDOOOOOOOOOWN!]]
->'''The Doctor''': Humans have got such limited little minds. I don't know why I like you so much.
->'''Sarah Jane Smith''': Because you have such good taste.
->'''The Doctor''': That's true. That's very true.

The one with the evil spotlight.

The TARDIS pitches up in Renaissance Italy (well alright, in [[UsefulNotes/{{Portmeirion}} Portmeirion]]), having had an encounter en route with a fizzy ball of energy that the Doctor calls the Mandragora Helix. He hasn't realised that he's brought it with him (since he rather stupidly left the door open), and when it escapes from the TARDIS and begins taking over or killing the locals, he follows.

The energy finds an underground temple and takes over the Cult of Demnos, which is led by court astronomer Hieronymous. It instructs them to prepare the way for Mandragora's full appearance. However, the astronomer himself is a pawn in political intrigues between Count Federico and his nephew, Duke Giuliano. Giuliano has just acceded to the Duchy of San Martino (after the last Duke rather mysteriously came down with a case of death) and a grand Masque will be held in honour. Giuliano and his [[HoYay companion]] Marco hope to prove that Hieronymous is a charlatan. Meanwhile, the Doctor is sidetracked by almost being executed and steals a few horses, and Sarah Jane is kidnapped and hypnotised by the cult.

During the dance, the Cult of Demnos attack the court and kill many, while Hieronymous -- now unified with the Mandragora Helix -- confronts the Doctor in the underground temple. Attempting to blast the Doctor with pure Mandragora energy, he is foiled when the Doctor reveals he has earthed both himself (with some iron armor) and the altar: the energy is drained off and the Earth is safe.

Also, Sarah becomes the first companion to question how come she can understand and be understood when the locals must all be speaking Italian. The Doctor says it's a "Time Lord gift", and it's later explained that it's done telepathically via the TARDIS.

!!Tropes:
* AllPropheciesAreTrue: Hieronymous predicts the death of the previous ruler with uncanny accuracy. And so he should, as Federico has poisoned him. When Federico decides that it's Giuliano's time to go, he orders Hieronymous to make another death prediction, mocking the astrologer when he insists his prognostications are real. His cult is able to accurately predict Sarah Jane Smith turning up, so it's implied they do have some ability, presumably assisted by Mandragora.
* AuthorAppeal: Louis Marks had been an academic historian before he became a writer. His specialist subject? Renaissance Italy.
* ArtisticLicenceHistory: Giuliano explains to Sarah his theory that the world is in fact round and not flat and that other scientists have started to accept this theory, repeating the common historical misconception that people living before 1492 thought the world was flat.
* {{Astrologer}}: Hieronymous.
* BeardOfEvil: Hieronymous has a glorious beard.
* BlackCloak: The cultists wear these, but Hieronymous opts for the purple pimp cloak and gold bling medallion seen in the image above.
* TheBlank: Hieronymous, after absorbing the Mandragora Helix.
* BloodlessCarnage: Giuliano and Federico both get wounded in swordfights, but not a drop of blood in sight. In Giuliano's case the Doctor even says he has to bandage him to stop the bleeding.
* BlueBlood: The Duke and his uncle the Count.
* BoundAndGagged: Sarah Jane.
* BrainwashedAndCrazy: Sarah Jane.
* ChosenOne:
* ColdBloodedTorture: But Marco still refuses to falsely confess.
* CoolMask: The cultists' gilded masks, especially the one Hieronymous wears.
* ContinuityNod: In the console room, the Doctor dusts with a frilly white undershirt like those worn by the Third Doctor, and Sarah picks up a recorder like the one played by the Second Doctor.
* {{Corpsing}}: During filming, Creator/TomBaker apparently made himself a nuisance by messing around off-camera in order to make Tim Piggot-Smith (as Marco) crack up during his torture scene.
* {{Cult}}
* DamselInDistress
* DragonWithAnAgenda: Hieronymous.
* DramaticUnmask: Federico gets quite a shock when he rips off Hieronymous' mask.
* EnergyBeings: The Mandragora Helix.
* EvilIsHammy: Oh, Hieronymous...
* EvilLaugh: The Helix does this, often when there is no other sign of its presence.
* EvilUncle: Count Federico.
* HeterosexualLifePartners: Giuliano and Marco, although the "heterosexual" is seriously debatable.
* HumanSacrifice: Sarah Jane is nearly sacrificed by the Cult of Demnos.
* LockedInTheDungeon: First Marco is locked in the dungeon, later on the Doctor, Sarah Jane and Giuliano join in on the fun.
* MalevolentMaskedMen: the Cult of Demnos.
* MasqueradeBall: The [[MalevolentMaskedMen Cult of Demnos]] takes advantage of Giuliano's swanky ascension party to conceal themselves in Part 4.
* TheMole: Sarah Jane is hypnotized into doing this.
* NotHerself / OutOfCharacterAlert: The Doctor knows Sarah has been taken over... because she's the first companion to ask how come she can understand people who speak other languages. Err, right...
** It makes sense. Sarah had been travelling with the Doctor for so long, if she was going to ask how she can understand people who speak other languages, she would have done it long before now.
* OffWithHisHead: The Doctor finds himself with his neck on the executioner's block in one cliffhanger.
* OOCIsSeriousBusiness: Sarah calls the Doctor out for this, telling him she knows when the situation has gotten apocalyptic because his jokes get more strained.
* ReasonableAuthorityFigure: The late duke.
* RebuiltSet: The serial introduces a Victorian-style "secondary control room" based around wooden panelling and copper metalwork, which managed to be totally {{Steampunk}} a good twenty years before the first stirrings of the movement. This tied into the "Film/HammerHorror" theme of the period. It was used for the whole of the season, but was unfortunately damaged beyond repair in storage afterwards, leading to a return to the old set.
* ReligionOfEvil: The Cult of Demnos.
* RoyallyScrewedUp: Count Federico. He has Giuliano's father killed to bring him one step closer to becoming the Duke of San Martino, but ends up being unable to have Giuliano assassinated.
* SecretCircleOfSecrets: The Cult of Demnos.
* SequelHook: The story ends with the Doctor revealing that the astronomical alignment that allowed Mandragora to attack Earth will recur towards the end of the twentieth century. This was not pursued in TV continuity, though several of the spin-offs have picked it up.
* SmugSnake: Both Federico and Hieronymous are arrogant would-be tyrants, but both are also convinced that they have more control over the situation than they do. Federico is so consumed with his schemes to overthrow his nephew that he ignores the real threat (the Cult of Demnos and the Helix) until it's too late; similarly, Hieronymous is a deluded fraud trapped by superstition and seduced by dreams of glory who ends up utterly consumed by the Helix.
* TheStarscream: Federico thinks Hieronymous is his loyal (but despised) underling. Hieronymous has other ideas,
* SwirlyEnergyThingy: The Helix itself.
* SwordFight: The Doctor merrily joins in.
* TapOnTheHead: When the Doctor realizes that Sarah Jane is being kidnapped and tries to intervene, a goon takes him out with a rock to his head.
* TargetedHumanSacrifice: Sarah Jane, who was apparently predicted to turn up.
* TranslatorMicrobes
* TrrrillingRrrs: "Hieronymous! You trrrrrrrraitor"!
* UnnecessarilyLargeInterior: Sarah Jane stumbles upon the Doctor's "boot cupboard", a massive room which has one pair of boots in it. When Sarah points out how absurdly large it is, the Doctor replies, "I've seen bigger boot cupboards."
* UnwillingSuspension: Marco is hung by his wrists while he's being tortured.
* WhenThePlanetsAlign: Hieronymous invokes this. He even appears to believe it.
* WhyDontYouJustShootHim: Averted; Federico [[TimeTravelersAreSpies thinks the Doctor is a spy]] and orders him taken out and executed.
* TheWisePrince: Giuliano.
* TheXOfY
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