Alan James

A saga of class relations and changing times in an Edwardian England on the brink of modernity, the film centers on liberal Margaret Schlegel, who, along with her sister Helen, becomes involved with two couples: wealthy, conservative industrialist Henry Wilcox and his wife Ruth, and the downwardly mobile working-class Leonard Bast and his mistress Jackie.

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.