Written by Johnny Byrne. This four-episode serial first aired January 31 to February 21, 1981.
Welcome to Traken, a world so perfect that evil can't survive! Seriously: any evil that tries to enter the atmosphere will literally crystalise out of the Trakenite air, ending up as a nugget of evil enclosed in a creepy humanoid statue with glowing red eyes.
And yet the Trakenites are good to the evil statues. They are so good that they assign people to look after the statues: bring them little bouquets of flowers, inquire after their families, persuade them to forsake wickedness, wipe off the bird poo, etc., until such time as the statue's residual sentience fades away, probably from sheer irritation. Then the stone crumbles into harmless dust and enriches the Trakenite soil.
But one statue was different. One statue contained an especially intractable malevolence, dubbed "Melkur", and its assigned guardian was a high-ranking Trakenite: Consul Kassia. Kassia's husband, Consul Tremas, was also a Traken elite, not to mention next in line for the Keepership; his daughter Nyssa was poised to carry on her family's august traditions. So, when Kassia was eventually corrupted by Melkur's malign influence, she was extremely well placed to wreak some serious damage to the Trakenite status quo.
Not that the planet's ruler, the kindly old Keeper of Traken, suspects The Mole in their midst. All he knows is that something is going pear-shaped, and he'd very much like the Doctor to drop by and help fix it. The Doctor is obliging, and soon he and Adric have made landfall—conveniently enough—right in front of Melkur!
They get hauled up in front of the Trakenite version of the Omniscient Council of Vagueness, where the Keeper is summoned again but only says "Evil! EEEEEEVIL!" Which, it must be admitted, does cast our heroes in a rather poor light. Thanks a lot, Keeper. Consul Tremas speaks up, protesting that the Doctor and Adric haven't been convicted of anything (yet, anyway); he gets rewarded by having them released into his custody and warned that his head is at stake if they misbehave.
Vicious group of people they got on this "perfect" world, isn't it?
Over in Tremas' quarters, we meet his daughter, Nyssa. She's been assigned to Melkur-visiting duty ever since her father and stepmother married, but she doesn't know that Kassia has been visiting it on the sly. Or that it's started talking to her, or given her a necklace that makes her evil.
Back in the Council Chambers, one of the interchangeable Consuls tries to commune with the Keeper to figure out what's going on, but the stress kills him.
Actually, Kassia kills him. Actually actually, the Melkur controlling her killed him, by shooting laser beams from her eyes.
Meanwhile, the Doctor, Tremas, Adric, and Nyssa run around trying to subvert the Melkur's evil plans. The Doctor discovers that the Melkur is actually a TARDIS and that the being controlling the Melkur is actually his archenemy, the Master. Who is still little more than a withered almost-corpse on the edge of death, seeking to use the powers of Traken to, well, not be a withered almost-corpse... and presumably get rid of the crusty black cloak while he's at it. Thing must smell awful by now, and we're not just talking about the Master's flesh. Dun-dun-dun.
The Master and the Doctor do their usual dance of trying to beat each other, and while the Doctor does keep the Master from taking over the Source (some sort of Hive Mind for Trakenites), the Master has the last laugh. He hijacks Tremas's body, freeing himself from the Kentucky Fried Time Lord he has been for the past four seasons and exulting in "a new body, at last," which somehow de-ages and becomes a sharp-dressed, slick-haired man in a goatee not unlike the late Roger Delgado (sure enough, the Expanded Universe would claim that the Delgado Master and the Crispy Master are one and the same). Just after the Master leaves in his disguised TARDIS, Nyssa enters, wondering where her father may be.
- Ascended Extra: Nyssa was originally created just for this story, but the producers saw potential for her character as a companion and wrote her into the following story (though she was phased into it rather than joining the Doctor right away).
- The Bad Guy Wins: The Master may not get control of Traken but he gets what he wanted most: a new body.
- Big Bad: The Master.
- Clothes Make the Maniac: Kassia is turned evil by the necklace the Melkur gives her.
- Cool Chair: The Keeper's throne.
- Corrupt Cop: Neman is pretty morally flexible when it comes to accepting bribes, something both heroes and villains take advantage of.
- Crystal Spires and Togas: Traken (though in this case it's more of an Elizabethan throwback combined with high technology).
- Death by Origin Story: Both of Nyssa's parents die as a result of the Master's machinations. Her stepmother Kassia, whom the Master manipulated, then killed once he had no further use for her, and her father Tremas, whose body he wears for the rest of the 1980s. As if that wasn't enough, her home planet is destroyed by the Master in the next story, completely by accident.
- Epiphanic Prison: Anyone who is evil and winds up on the planet becomes imprisoned in a stone form called a "melkur" by the anti-evil effects of the area (It Makes Sense in Context). "Melkur" is their word for a fly trapped in honey. To be freed, all you have to do is not be evil anymore. Once your heart changes, you're free. Naturally, The Master had been stuck for a good long while. Not. The Melkur is really his TARDIS, whose chameleon circuit works just fine. He's been free and able to orchestrate the evilness that had been going on all along. He probably avoided actually becoming a melkur by staying inside and moving it wherever he needed to be, as the Melkur was sometimes seen to move.
- Even Evil Has Loved Ones: As warped as Kassia has become by the Master's manipulations, she genuinely cares for Tremas, and a lot of her actions are the result of not wanting him to take up the mantle of the Keeper (and thus be separated from her forever).
- Evil Redhead: Kassia, after her Face–Heel Turn.
- Eye Beams: The Melkur can do this, and transfers the power to Kassia later.
- Flowers of Romance: Kassia became gradually infatuated when she was a child to the Melkur (giving flowers to the humanoid). However, the Melkur turned out to be The Master, who manipulated her into killing and manipulating others in order to achieve the Keepership.
- Grand Theft Me: Tremas's body gets stolen by the Master.
- Hijacked by the Master: Contrary to the beliefs of some fans, people who watched this story unspoiled do claim to have been surprised when the Master was revealed.
- Honour Before Reason: The Doctor asks Tremas to share his knowledge of the Source so they can figure out how to defeat the Melkur, and Tremas replies that he can't, because he swore an oath as Consul to safeguard the secrecy of the Source's workings. The Doctor says sharply that in that case Traken is doomed, but not to worry, at least Tremas's honour will be intact. After an inner struggle, Tremas allows himself to be persuaded.
- It Was Here, I Swear!: When the Trakenites go to where the TARDIS landed to verify the Doctor's story, it's vanished.
- Jackass Genie: Kassia's desire that leads to her downfall is that her husband Tremas should not become the Keeper (and thus be separated from her, because whoever becomes the Keeper must abandon all their mortal ties). The Melkur promises that he will prevent Tremas from becoming the Keeper, and he does — by forcing Kassia to become the Keeper instead.
- Just One Second Out of Sync: How the Melkur hides the TARDIS from the Doctor and the Trakenites.
- Karmic Death: Kassia ends up selling out her entire society to the Melkur due to a combination of Love Makes You Evil and Love Makes You Stupid. Once she stops being useful, she gets what she so richly deserves.
- Lighter and Softer: Compared to the last Crispy Master-centric serial, this one is far less violent and features none of the political commentary and psychological horror of its predecessor. If anything, it's far closer to the kind of story that Roger Delgado's original take on the Master would've featured in.
- Living Statue: The Melkur turns out to be the Master's TARDIS, with the Master stuck inside.
- Love Makes You Evil: Kassia is tricked into serving the Melkur because she doesn't want to lose Tremas.
- Meaningful Name: Tremas. His body is taken over by the Master, whose title is a Significant Anagram of "Tremas". The Master frequently used aliases related to his name— Colonel Masters, Reverend Magister, Professor Thascalos— but usually he had a chance to pick them himself.
- Nightmare Face: The Master. He gets a new one at the end.
- The Nth Doctor: Geoffrey Beevers takes over as the Master, only for Anthony Ainley to take over at the story's end.
- Not Using the "Z" Word: The Master is only called by his name once in the story, and neither actor who plays him is credited as such.
- Oh, Crap!: The Doctor, when he's informed that the Fosters couldn't find the TARDIS in the grove.
- Reasonable Authority Figure: The Consuls are generally this, especially Tremas and Seron. Not so much Kassia, though, and the others seem a bit naive about the possibility of evil within their society. It never occurs to them to question some of Kassia's claims.
- Red Eyes, Take Warning: The Melkur has these, and combined with his voice you know right away he's a baddie. Kassia gets them later on.
- Replacement Artefact: By the time he left the series in "Warriors' Gate", the previous story, half of K-9's function was stunning opponents for the Doctor with a red laser beam from his "nose cannon". So what do we see the Doctor doing in this story? Stunning opponents with a green laser beam from an "ion bonder" nicked from Nyssa. The device is used again in "Castrovalva" before getting waterlogged and removed from the story. It presages the producer-mandated destruction of the sonic screwdriver later, which also led writers to introduce various one-off gadgets that served exactly the same narrative purpose as the original screwdriver.
- Sarcasm Mode: When going through the Doctor's logs, Adric mentions his handwriting, prompting the Doctor to ask "What about my handwriting?" Adric just replies, "Marvellous."
- Sealed Evil in a Can: Unfortunately the can isn't as sealed as everybody thinks.
- Significant Anagram: Averted, unusually enough for Doctor Who. "Tremas" is an obvious enough anagram for "Master", leading the viewer to think he's a baddie— but he is a good man and a staunch ally of the Doctor throughout. Not shockingly, the name of "Tremas" was demanded by producer John Nathan-Turner because actor Anthony Ainley, who played the character, would be playing the Master soon enough. Reflecting back on it, most of the cast think that it was a pretty silly reason for the name.
- Unfit for Greatness: Subverted. Luvic has this opinion of himself and so rules himself out for the Keepership. When the post needs filling in an emergency, though, he finds his fitness.
- Wham Shot: Two in quick succession. After Melkur has been seen walking around a few times, and revealing that someone is looking through its eyes on video screens, its operator swings round to face the camera, revealing that it's the Master. The very next shot is of the Melkur, revealing its true nature by dematerializing with the familiar TARDIS sound effect.
- Wicked Stepmother: Kassia has shades of this.
- The X of Y
- You Are Too Late: The Doctor tells Melkur that they're going to stop him, and Melkur replies that he's too late. Moments later, Melkur gains control of the Source.
- You Can Talk?: Kassia has an almost romantic fixation on the Melkur, but even she is shocked when it starts to talk back to her.
- You Have Failed Me: Melkur has Neman executed for his chronic inability to keep the Doctor imprisoned.
- Your Princess Is in Another Castle!: At the end, the Master has been defeated and possibly killed and the Doctor has left. Then the Master reappears, kills Tremas and gains a new body, and it turns out to be the first part of a trilogy.