The Citadel

In a citadel on the planet Peladon, Chancellor Torbis reports to King Peladon that the delegate from Alpha Centauri has arrived. Peladon wants the planet to join the Galactic Federation but Hepesh, his High Priest, is against such a move. Peladon has invited a committee of assessment to the planet to decide on the issue and all are now present, barring the chairman delegate from Earth. Torbis leaves to inform the other delegates of Alpha Centauri's arrival but he is attacked and killed by Aggedor, the sacred and mythical beast of Peladon.

The TARDIS arrives on the slopes of the mountain on which the citadel is perched, and when The Doctor and Jo Grant exit, it tumbles to the bottom of the mountain. Unable to descend, The Doctor and Jo struggle up the mountainside through rain and wind until Jo finds a cave which leads to a series of underground tunnels under the citadel. They soon find their way into the citadel and see an Ice Warrior lumber past just before they are caught and taken to the throne room.

There, they meet Peladon and the assembled delegates: Alpha Centauri, Arcturus and Martians Lord Izlyr and his aide Ssorg. Izlyr assumes that The Doctor is the delegate from Earth and the others follow suit. The Doctor, not wishing to cause undue trouble, plays along by introducing Jo as ‘Princess Josephine of TARDIS’. Peladon is very taken with Jo. While they are talking, Hepesh gestures to Grun, the King's champion, and he slips out of the throne room and positions himself to topple a statue of Aggedor onto the delegates as they leave the throne room.

King Peladon

Luckily, The Doctor sees the statue as it falls and pushes the delegates out of its path just before it crashes to the floor, saving their lives. Un-noticed Grun creeps back into the throne room and while Peladon tries to assure everyone that there is no need for alarm and that they are all safe, Jo slips away and finds a piece of electronic equipment near where the statue was originally standing. Later, when she shows it to The Doctor he confirms that it is an electronic key made from Trisilicate, which can be found only on Mars, home of the Ice Warriors.

Arcturus is then attacked. Lukily The Doctor is able to re-route his circuits and stabilise his condition. In doing so he discovers that someone has taken a servo junction unit from his life support systems. Jo decides to investigate and it is not long before she finds the missing unit in the Warriors' room. However, she is discovered by Ssorg who locks her in the room. Jo though manages to escape by climbing out of the window and edging round to another room. On entering the corridor she sees Aggedor and, panicking, runs straight into Izlyr and Ssorg. She talks with the Martians and realises that they are innocent.

High Priest Hepesh

Meanwhile The Doctor has been lured into the tunnels under the citadel by Grun and is chased by Aggedor. He arrives at the sacred temple of Aggedor and Hepesh has him arrested for sacrilege, a crime for which there is only one punishment - death. Jo, on learning what has happened to The Doctor, appeals to Peladon and he commutes the sentence to a battle to the death with Grun.

Hepesh offers to help The Doctor escape and gives him a map of the tunnels. He tells him that he does not stand alone in his desire to prevent the planet from joining the Federation. The Doctor fits a mirror to the top of his sonic screwdriver and leaves. In the tunnels, the map leads him to Aggedor. The Doctor hypnotises the beast with the spinning mirror and by crooning a Venusian lullaby. However, Jo, who has followed The Doctor, frightens Aggedor off with a flaming torch, and they return to tell Peladon that Aggedor is real but he does not believe them and the trial by combat takes place.

The Doctor beats Grun, but refuses to kill him. Arcturus points his laser weapon at The Doctor, but Ssorg destroys Arcturus before he can fire. Hepesh escapes into the tunnels and recruits the guard captain and some of the guards to fight against Peladon. The delegates discover that all their communicators have been destroyed and they are unable to summon help.

Alpha Centauri

It is not long before Hepesh and his guards storm the throne room and fight with Peladon's guards. This prompts The Doctor to search for Aggedor again. On locating the beast he hypnotises Aggedor and brings him to the throne room where he attacks Hepesh and kills him. With this, the guards surrender so ending the conflict.

With peace resumed The Doctor and Jo find the TARDIS in one of the citadel rooms where it had been placed earlier by Peladon's men. As they wait for the coronation is about to take place The Doctor muses that it was no coincidence that they landed on Peladon at this crucial moment in the plants history. He therefore correctly deduces that again the Time Lords have brought them here at this time and so the TARDIS is still not within The Doctor's control. Then just before they join the others to watch the coronation the real delegate from Earth arrives and The Doctor and Jo decide that it would be best if they left quickly now that it has been revealed that they are not who everyone thought they were…