[[quoteright:350:http://static.tvtropes.org/pmwiki/pub/images/meglos_5505.jpg]]
[[caption-width-right:350:Just... Just look at the panic in Tom's eyes, there...]]
->''"First things first, but not necessarily in that order."''
-->--'''The Doctor'''

The one with an evil cactus.

On the planet Tigella, life revolves around the Dodecahedron, a mysterious alien artifact which powers Tigellan civilization. Some Tigellans worship it as a gift from their god, while others consider it just an object to be scientifically studied. With tensions between the two groups running high, the Tigellan leader sends a message to the Doctor, who has visited Tigella once before, inviting him to come and arbitrate between them.

The message is intercepted by Meglos, the last survivor of the neighbouring planet Zolfa-Thura; the scientifically-advanced Zolfa-Thurans created the Dodecahedron shortly before wiping themselves out in a massive war. Meglos uses his technology to trap the TARDIS in a time loop and then to disguise himself as a double of the Doctor, and travels to Tigella himself. He manages to steal the Dodecahedron and is about to leave when the real Doctor, having escaped the time loop, arrives and is promptly accused of the theft. There is much confusion, and although it becomes clear that there are two Doctors roaming about, the fake Doctor manages to get away with the Dodecahedron. Meglos returns to Zolfa-Thura, where he plans to use the Dodecahedron to power a superweapon capable of destroying entire planets.

The Doctor and Romana follow, and the Doctor attempts to turn his trick against him by telling Meglos's hired henchmen that ''he'' is Meglos and that any other Doctor they see about the place is the real Doctor and should be locked up. This works long enough for him to mess around with Meglos's superweapon, and when it is fired it explodes, taking Meglos, his henchmen, and the planet of Zolfa-Thura with it.

Oh, and the Dodecahedron, leaving Tigellans of all ideological persuasions to work together to rebuild their civilization using some other power source.

[[http://www.dailymotion.com/video/x9nzb0_meglos-part-1_shortfilms Can be watched here.]]
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!!Tropes:
* AllThereInTheManual: The "abducted earthling" of the televised story is given a name in the novelisation George Morris and a backstory as an assistant bank manager. His abduction by the Gaztaks, whom he believes at first are students carrying out one of their Rag Week pranks, is shown in the opening pages.
** The novelisation makes it clear the "Gaztak" is a broad term for mercenary bands, not referring only to Grugger's group.
** The novel answers the question of how Meglos' species would be able to advance technologically as immobile cacti by their ability to take over the minds of other beings, implying that, despite what was shown, they are able to do it without technological adjuncts.
** The novelisation ends with George Morris returning to Earth.
* BadBadActing: The solution to the time loop.
* ChekhovsGun: Romana is attacked by killer plants. Not only does this separate her from the Doctor for most of the story, she leads Meglos' henchmen back to the plants, and uses them attacking as a distration to escape.
* ChronicBackstabbingDisorder: Meglos anticipates his allies betrayal, and establishes the ground rules straight off.
* FightingFromTheInside: Meglos kidnaps a mild-mannered, terrified human from 20th century Earth and possesses his body. Unfortunately for Meglos he proves to be tougher than he looks.
* GroundhogDayLoop: {{Defied|Trope}}. The two Time Lords solve a time loop within 5 minutes before starting the adventure proper. But then, they are ''Time Lords'', it should be easy for them.
* HeroicBystander: George Morris (aka The Earthling) proves that despite his {{geek}}iness and NerdGlasses, that he's just a pinch TooSpicyForYogSothoth.
* HumanSacrifice: The Doctor is offered up to Ty almost.
* ImpersonatingTheEvilTwin: The Doctor impersonates Meglos. He is discovered only when Meglos is shot in the belief that he's the Doctor and replies, "satisfied?"
* KickTheDog: Literally when the mercenary kicks K-9. According to the commentary, the actor, who was best known for playing hammy villains, added this business himself because he figured the fans would be expecting it.
* {{Leitmotif}}: The titular angry cactus is signalled by a vibraslap scream, with increasing distortion as he approaches VillainousBreakdown.
* ManEatingPlant: The plants that attack Romana and later, Meglos' henchmen.
* NamesToRunAwayFromReallyFast: Meglos
* OurMonstersAreWeird: Meglos. A dangerous and psychotic alien DiabolicalMastermind, technocrat and shapeshifter, who accomplished all this despite being a sessile cactus with no discernable sensory organs.
* PlantAliens: The titular Meglos, an evil shape-shifting ''cactus'' who wanted to take over the universe. [[IncrediblyLamePun What a prick]].
* PlayingPossum: One of the pirates.
* ProtagonistCenteredMorality: The Doctor's decision to kill Meglos and the band of thieves he was working with (who didn't even know they were involved in a genocidal scheme up until the end) is never explained or even questioned. More alarmingly, the underground city leaders thank the Doctor for saving their planet from destruction and stopping the criminal who stole their power source, but never question whether it was really necessary to destroy the power source. They now have to evacuate untold cubic miles of powerless underground dwellings, set up new homes in a horrible writhing jungle, and somehow find the power to make it all work. Assuming this is even possible, it will be a long and difficult process in which many lives will no doubt be lost. The Doctor may have had no alternative to destroying the artefact, but we wouldn't know because the subject is never discussed at all.
* RecycledSoundtrack: The sound effect created for the approach of [[Recap/DoctorWhoS15E3ImageOfTheFendahl the Fendahl]] is re-used as background atmosphere for the Tigellan jungle, as well as effects used in [[Recap/DoctorWhoS3E4TheDaleksMasterPlan The Daleks' Master Plan]] and [[Recap/DoctorWhoS10E4PlanetOfTheDaleks Planet of the Daleks]].
* SignificantAnagram: Brotadac is an anagram of "Bad Actor".
* SingleBiomePlanet: Tigella is a jungle planet. Zolfa-Thura is a desert planet (although it has the excuse of having suffered a life-extinguishing catastrophe).
* TerminallyDependentSociety: The people of Tigella live in a city where everything is powered by a single alien artifact, which gets destroyed at the story's climax; although they're initially horrified by having to manage without it, it's presented as ultimately being an opportunity rather than a disaster.
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