On the planet Shem a mysterious unseen force called the Power binds together three diverse sentient humanoid lifeforms; a race with monkey-like faces, a three-armed race called the Monashem, and a race of winged warriors called the Ragashem. The ruler of Shem alone knows the secret of the Power. Azu, Supreme Ruler of all Shem has died, leaving the crown to his daughter, Princess Azula. The tribes of Shem have gathered for Azula's coronation, but at the coronation the leaders of the other two races, Orga and Zig, make a bid for the Power, and combat breaks out. But one guest is late in arriving - the Doctor. The Fourth Doctor and Leela find themselves thrown into the midst of a conflict. The contestants: Orga, leader of the Monashem, Zig, leader of the Ragashem, and Azula, heir to the throne of Shem. The prize - the Power!
Conflict breaks out at the coronation of Princess Azula as Supreme Ruler of Shem. The TARDIS materializes in the midst of the melee, allowing Zig to slay Orga, leader of the Monashem, and Azula to escape, aided by her champion. When the Doctor asks what is going on, Zig declares that he is now ruler of all Shem, and that he will put the Doctor and Leela on trial. But this trial is a "nightmarish perversion of justice degdged up from the depths of Zig's power-mad brain." Concluding that the TARDIS is proof that the Doctor has access to the Power, Zig tells the Doctor that unless he divulges the secret of the Power, he will be found guilty, and Leela will be fed to the porgs - deadly Shemian fighting swine with specially sharpened teeth. The trial itself involves the Doctor being cast into a pit where he faces the prosecution - giant savages armed with iron hammers. There are too many, the Doctor cannot fight them off!
In the nick of time he is reminded by Zig's words that he has on his person a present for Azula - an anti-gravity belt. Meanwhile, Azula decides that she will return to save the Doctor, who was one of her father's closest friends.
Zig is about the release the Porgs, but just in time, the Doctor flies out of the pit, awkwardly trying to manouever using the anti-gravity belt. "Look! He flies with no wings!" someone cries. "So the Power makes you fly, Doctor!" Zig exclaims, drawig his sword. "Let us see how well!" spreading his wings, the power-crazed winged warrior takes to the skies. "I, Zig, am the finest airborne warrior in all of Shem. Prepare to die!"
Zig has no trouble catching the Doctor, and soon has this sword at the Doctor's neck, but at that moment, Azula returns. "Hold, Zig! Let him be!" Azula has the secret of the Power, in a book, and she declares that her father was wrong to keep it from the people. She will give the secret of the Power to everyone, believing that it is the only way that peace can be brought to the warring tribes of Shem. "No! The Power must be mine! It must be mine alone!" cries Zig, swooping towards the Princess with his sword upraised to strike her down.
The Doctor diverts the anti-gravity beam of the belt into Zig's flightpath, blasting him away from the Princess and into the pit where the "prosecution" are. "My wings... too wide... can't..." The judge meets the prosecution.
With Zig and Orga dead, the Coronation can at last take place, and Azula, Ruler of all Shem, tells the people, "This book holds the secret, but the Power itself is in each and every one of you. Use the Power wisely, and with love we shall all prosper together. Long live Shem!" The Shemites hail their new, wise ruler. "Hear, hear!" the Doctor comments.
to be added
- The Doctor is called Dr. Who in a caption when first leaving the TARDIS.
- The Power bears more than a passing resemblance to the Force as described in the film Star Wars released in 1977.