The one where the Doctor massages a penis monster.
The TARDIS follows a distress signal to the planet Chloris, where the Doctor and Romana investigate what appears to be the shattered remains of an enormous metal egg. (The Doctor's technique largely involves listening to the sound made when he taps it with a teaspoon.) They are captured by guards and taken to see the local dictator, Lady Adrasta, who owns the mine that is the planet's only source of metal. Adrasta is impressed by how much the Doctor has figured out about the egg, and wants him to work for her; the alternative is to be thrown into the Pit, an abandoned mine working inhabited by a mysterious Creature that kills all who come near.
The Doctor being the Doctor, he jumps into the pit with both feet, and soon meets the Creature. It can't talk, so the Doctor resorts to cuddling with it and extensively putting his mouth on its... large bits that stick out. Once the Creature manipulates some local beardy men into retrieving its communicator, it's able to use the Doctor's own voice to speak, and the Doctor discovers that it is in fact an alien ambassador from the planet Tythonus, whose spacecraft was the egg investigated earlier. Tythonus has lots of metal but not much vegetation, and the ambassador had hoped to organise a trade, and was thrown into the pit for his trouble — Adrasta's stranglehold on metal production is keeping her in power.
The Doctor helps the ambassador to escape, and in return the ambassador helps the Doctor to divert the neutron star that the Tythonians have aimed at Chloris in retaliation. Adrasta is killed by the ambassador, and a trading contract is drawn up.
- Astrologer: Organon was an itinerrant Court Astrologer, until Lady Adrasta threw him down the pit.
- Aside Glance: The Doctor forces Lady Adrasta's hand onto Erato's larynx machine and the creature starts speaking through her. As she goes through her Villainous Breakdown, we can see the Doctor lurking at the edge of the shot, looking straight at the camera out of the corner of his eye and smirking.
- Big "NO!": Adrasta at the pt. 3 cliffhanger.
- Bond One-Liner: Karela sticks a knife in Torvin while he's gloating over his hoard of metal, and tells him, "There's another six inches to add to your collection."
- Characterization Marches On: This was the first story that Lalla Ward filmed as Romana and the script had her playing Mary Tamm's incarnation, even wearing a similar white dress.
- Continuity Nod: A number of the Doctor's old costumes appear on the TARDIS hatstand. His coats from "The Seeds of Doom" and "The Talons of Weng-Chiang" are two of these.
- Corpsing: During the scene where the Doctor has to approach a monster that looks like a giant green penis and scrotum and "communicate" with it, Tom Baker, normally very good at keeping a straight face during such things, is clearly about to crack up and even has to hide his smile with his hand at one point.
- Curse of Babel: The titular creature is presented as a villain until we find that it just lacks a speech synthesizer.
- Distress Call: What kicks off the episode is the Doctor responding to one of these.
- Exactly What It Says on the Tin: There's a running joke about the straightforwardness with which Adrasta names things: There's a creature, which is called "the Creature", in a pit, which is called "the Pit", and also a place that's an automatic death sentence for anybody found there, which is called "the Place of Death".
- Expy: Torvin was clearly modeled on Fagin.
- Foreshadowing: The Doctor claims a ball of string Romana finds in the TARDIS helped Theseus and Ariadne out of the Minotaur's maze. This may have been foreshadowing "The Horns of Nimon".
- Forgot About His Powers: The Doctor finds himself at the bottom of the titular pit, and wants to climb out. So he takes out of his pocket a book to help people climb Mount Everest. The book is in Tibetan...so he takes out a Tibetan learning book, also from his pocket. While this is not often touched upon in the classic series, the Doctor should be able to understand Tibetan thanks to the Tardis's Translator Microbes. It is probably just Rule of Funny, though.
- HeelFace Turn: The Huntsman spends most of the story leading his wolfweeds on Adrasta's behalf. When he learns the truth, however, he becomes the first of his people to turn against her and refuses to turn the wolfweeds on the Doctor.
- I Like Those Odds: When Romana calculates their odds of success at 740,384,338 to one against, the Doctor claims that this is his lucky number.
- Lady Land: Chloris is a matriarchy, although under Lady Adrasta it's somewhat autocratic in general.
- Meaningful Name: The Creature in the Pit is called Erato, which means "sexually desired" and is the name of the muse of erotic poetry in Greek mythology. In the story, Erato is a force of love and creativity. And, more prosaically, it looks like a giant cock and balls and Tom Baker's acting exploits this for all it is worth.
- Metal-Poor Planet: The story takes place on the planet Chloris which has an over-abundance of plant life and virtually no metal; the local dictator's power comes from having control of the only mine.
- Only Electric Sheep Are Cheap: In an inorganic variant, the bandit chieftain waxes rhapsodic about the amazing treasures his group has stolen: precious items of iron, zinc, and even nickel! Needless to say, this scene takes place on a metal-poor planet, where only members of the elite can boast such prizes.
- Phony Psychic: Organon
- Plant Aliens: The mobile, carnivorous wolf-weeds.
- Reality Is Unrealistic: Although the Doctor's solution to the problem of the neutron star, weaving a shell of aluminium around it, has been criticised as silly, the idea was in fact proposed to David Fisher by members of the Institute of Astronomy, Cambridge.
- Shout-Out: Two character names were inspired by Greek Mythology:
- Lady Adrasta was inspired by Andromeda, who attracted a sea monster which plagued her homeland.
- Erato was one of a group of goddesses called the Muses, specifically the Muse of erotic poetry; significantly, her name means lovely.
- The story's setting, Chloris, came from chlorophyll, the green pigment found in most vegetation.
- Sickly Green Glow: The Creature; more or less justified by its Bizarre Alien Biology
- Single-Biome Planet: The jungle world of Chloris
- Specific Situation Books: While trying to climb out of the Pit, the Doctor produces a book from his pocket called Everest in Easy Stages. Sadly, it's in Tibetan, so he produces another book called Teach Yourself Tibetan.
- Stellar Name: "Adrasta" is one letter off "ad astra", Latin for "to the stars" (as in "Per Ardua Ad Astra", "Through adversity to the stars", the motto of The Royal Air force).
- Terms of Endangerment: Adrasta rarely misses a chance to call Romana "my dear", usually while simultaneously holding a sword to her throat. Or slapping her across the face. And occasionally while she's tied to a chair. Or all three.
- Western Zodiac: In Space! Organon's astrology. The Doctor, when asked what sign he was born under, replies that he was born under a sign bearing the logo of the Gallifreyan Maternity Service.
- Your Princess Is in Another Castle!: Lady Adrasta is killed with about 20 minutes to go, seemingly leaving the Doctor to simply arrange a treaty between Chloris and Tythonus. Then the Tythonians decide to destroy Chloris in retribution for her actions and various minor villains get in the way of the Doctor trying to stop them.