Doctor Who: The Curse of Peladon (1972)

The planet Peladon has applied to join the Galactic Federation, and The Doctor is mistaken for the chairman of the committee sent to assess its application, while Jo is taken for an Earth princess, with the mythical curse of Aggedor apparently striking chancellor Torbis dead, The Doctor must discover who is desperate to stop Peladon joining, but soon he is sentenced to death and his only Allies seem to be Jo and the Ice Warrior Delegates.