The Doctor and Jo arrive on the medieval planet Peladon, where the Doctor is mistaken for the Earth Delegate of the Galactic Federation and Jo is mistaken for a princess. Where the Doctor uncovers a conspiracy, as he exposes the evil scheme of the high-priest Hepesh who bids to prevent King Peladon from joining the galactic Federation.

The Doctor is sentenced to fight Grun to the death and his attempt to escape leads to an encounter with Aggedor.