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.
Unfortunately the movie Doctor Who: The Keys of Marinus is not yet available on HBO Max.
| Directing | John Gorrie | Director |
| Writing | Terry Nation | Writer |
| Writing | David Whitaker | Script Editor |
| Production | Verity Lambert | Producer |
| Sound | Norman Kay | Music |
| Production | Mervyn Pinfield | Associate Producer |
| Costume & Make-Up | Jill Summers | Makeup & Hair |
| Costume & Make-Up | Daphne Dare | Costume Design |
