Inspired by Virginia Woolf, a young writer worries that marriage will hinder her literary ambitions. The film includes extracts from Virginia Woolf's novel To the Lighthouse and her essay Professions for Women, both read by feminist filmmaker and theorist Laura Mulvey.

The Doctor and his companions are pursued through time and space by the Daleks on the desert planet Aridius and beyond.

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.