The TARDIS arrives on the planet Marinus on an island of glass surrounded by a sea of acid. The travellers are forced by the elderly Arbitan to retrieve four of the five operating keys to a machine called the Conscience of Marinus, of which he is the keeper. These have been hidden in different locations around the planet to prevent them falling into the hands of the evil Yartek and his Voord warriors, who plan to seize the machine and use its originally benevolent mind-influencing power for their own sinister purposes.
William Hartnell
The Doctor
Carole Ann Ford
Susan Foreman
Jacqueline Hill
Barbara Wright
William Russell
Ian Chesterton
George Coulouris
Arbitan
Martin Cort
Voord / Warrior / Ice Soldier / Aydan
Peter Stenson
Voord / Ice Soldier / Second Judge
Gordon Wales
Voord
