There is no plot! I am being completely honest with you.
— King Peladon is perhaps being a little harsh on the writers.
The Doctor thinks he's managed to fix the TARDIS at long last. Taking a test flight, he and Jo find themselves on the planet of Peladon, where a new king is about to be crowned and the Galactic Federation are assessing the planet for entry. Only the human delegate is missing - so of course the Doctor is immediately assumed to be him, a role he dives into with enthusiasm.
The other committee members - the giant, camp, eyeball-octopus-thing Alpha Centauri, Arcturus, the Ice Warrior lord Izlyr and his subordinate, Ssorg - are worried about the death of Chancellor Torbis, the new king's advisor. High Priest Hepesh opposes entry into the Federation and attributes Torbis's death to the displeasure of Aggedor, the sacred monster of Peladon. The Doctor, meanwhile, concludes that a saboteur is at work.
Initial suspicion naturally falls on the Ice Warriors - after all, they've been villains twice already - but of course it's Hepesh himself. Arcturus, one of the delegates, has convinced Hepesh that the Federation will exploit Peladon for its mineral wealth, whereas in reality his own government plan to do so once Peladon has rejected entry. Ssorg, defending the Doctor, kills Arcturus, but Hepesh gets away, fleeing into a network of tunnels behind the giant statue of Aggedor.
Hepesh leads a coup and attempts to force the king to reject entry into the Federation once and for all. The Doctor arrives with the real Aggedor, a mountain beast thought extinct which Hepesh had trained to obey him, and which he had used to spread the story of the curse. Hepesh orders Aggedor to kill the Doctor. But the Doctor has already met and befriended Aggedor, who turns on Hepesh instead.
- Alas, Poor Villain: Hepesh's death seems to devastate everyone present, especially Peladon.
- Arranged Marriage: The other alien delegates believe that this is why "Princess Jo" has accompanied the Doctor. Jo later sets them straight.
- Bait-and-Switch Gunshot
- Big Bad Duumvirate: Arcturus and Hepesh.
- Bookcase Passage: Just about any torch on the wall can be lowered to activate a secret door.
- Boy of the Week: There is definite romantic tension between King Peladon and Jo, despite him angering her with an overly-hasty proposal.
- Brains and Brawn: The Doctor and Grun.
- Brain in a Jar: Arcturus.
- Deadpan Snarker: Princess Jo complains of the incompetence of the pilot who caused them to crashland on this planet, while the Doctor rolls his eyes in the background.
- Duel to the Death: The Doctor has a choice: be executed for defilement of Aggedor's shrine or fight Grun to the death. He chooses the latter, but doesn't kill Grun when he wins.
- Does This Remind You of Anything?: Alpha Centauri
- Evil Chancellor: Well the chancellor isn't evil, but the High Priest fits the role.
- Fantasy Counterpart Culture: This story is an analogy of Britain joining the EEC.
- In the DVD commentary, both Terrance Dicks and Barry Letts deny there was any deliberate message in the storyline, while admitting that it's entirely possible that the author may well have been inspired to write his story by the political debate at the time.
- Gentle Giant: Aggedor, once the Doctor calms him down.
- I Owe You My Life: The Martian ambassador sides with the Doctor after the Doctor saves all delegates' lives.
- Hard Head: Grun is merely unconscious for maybe a minute after he's bashed on the head with a rock.
- Lord Country: The ambassador to Alpha Centauri is named "Alpha Centauri".
- So is Peladon, king of Peladon.
- Mistaken Identity: the Doctor is assumed to be the delegate from Earth.
- Music Soothes the Savage Beast: Aggedor is calmed by the Doctor singing a Venusian lullaby.
- Not Always Evil: The Ice Warriors. Although they initially come across as potential villains, they turn out to have developed into a peaceloving race... although they still have weapons in case diplomacy doesn't work.
- No Sell: Grun isn't impressed when the soldiers punch him. A rock on the head, however...
- Proud Warrior Race Guy: Possibly Grun, definitely Izlyr (and presumably Ssorg).
- Punch! Punch! Punch! Uh Oh...: Happens when a soldier attempts to stop Grun, the King's Champion. He punches Grun several times to no effect.
- The Radio Dies First: Well, it's destroyed deliberately first.
- Real After All: Aggedor.
- The Reveal: The Martians are the good guys here.
- The Speechless: Grun, a mute, and a reasonably heroic one once outmaneuvered by the Doctor.
- Title Drop / Running Gag: When the real Earth delegate shows up, she asks: "Doctor who?"
- Took a Level in Kindness: When Jo ruins the Doctor's promising hypnosis of Aggedor, the Doctor, annoyed, tells her what he was doing, but forgives her a minute later and they move on. It mirrors their first meeting when she ruins his experiment and he berates and insults her, and shows how far their friendship has gone in the time they spent together.
- Well-Intentioned Extremist / Knight Templar: Hepesh. But we do learn eight Doctors later that the Strawman Has a Point, spelled O-O-D.
- The X of Y
- Zettai Ryouiki: Unusual male example in King Peladon.