Parts: 4
Writer: Brian Hayles
Airdates: 29 January 1972 - 19 February 1972
Production Code: MMM
Creature Feature: Aggedor, Ice Warriors, Alpha Centauri, Arcturus
Story: With his ability to use the TARDIS restored, the Doctor persuades Jo to accompany him on his first trial run. But his assurances of making it back to Earth within minutes prove hollow, as they exit the ship to find themselves on a windswept mountain ledge. When the TARDIS topples down the cliff, the Doctor and Jo have only one option: climbing to the castle jutting from the rockface above.
When they finally reach the castle, they quickly find themselves plunged into an interplanetary situation: they have arrived on the planet Peladon, which is seeking entrance into the Galactic Federation, and the king is being visited by delegates from various planets who intend to assess Peladon's suitability for admission. The Doctor is mistaken for the absent delegate from Earth, and as only royal females are permitted in the king's presence, Jo takes on the role of Princess Josephine of TARDIS with aplomb.
But someone on Peladon is determined to prevent the planet from entering the Federation...and to make sure such an event never takes place, they are willing to kill the delegates, one by one. Can the Doctor and Jo maintain their secret identities long enough to uncover the traitor and assure Peladon's entrance into the Federation...or will they merely become two more casualties?