An energy drain traps the Third Doctor and Sarah Jane Smith on the planet Exxilon with its hostile natives, causing the travellers to make an uneasy alliance with a Marine Space Corps expedition and a squadron of Daleks. The key to escape for all of them lies at the heart of a powerful and mysterious lost city, but only after a series of deadly traps.

• BBC
• Jon Pertwee
• Elisabeth Sladen
• Duncan Lamont
• John Abineri
• Joy Harrison
• Julian Fox
• Neil Seiler
• Arnold Yarrow