
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.
Social & External

The Doctor

Susan Foreman

Barbara Wright

Ian Chesterton

Arbitan

Voord / Warrior / Ice Soldier / Aydan
Voord / Ice Soldier / Second Judge
Voord
Altos

Sabetha

Voice of Morpho (voice)
Darrius
Vasor

Ice Soldier / Larn
Ice Soldier / First Judge / Guard
Ice Soldier

Tarron
Senior Judge

Kala

Eyesen

Yartek
Eprin (uncredited)