The Time Lords send the Doctor and Jo on a mission to deliver a sealed message pod to an unknown party aboard a Skybase orbiting the planet Solos in the 30th century. They are caught quickly in a power struggle between the cruel Marshal of Solos and the young Solonian Ky over the future of Solos - a future that hinges on the contents of the message.

• BBC
• Jon Pertwee
• Katy Manning
• Paul Whitsun-Jones
• James Mellor
• Garrick Hagon
• Christopher Coll
• George Pravda
• John Hollis