The TARDIS lands in a primeval forest, and the Doctor meets Leela, a warrior banished from her tribe. He learns that an ongoing war between the Sevateem and the Tesh was instigated by Xoanon, the god they both worship. In reality, an all-powerful computer, Xoanon, is possessed by a desperate madness directly related to the Doctor - one which only the Time Lord can rectify! In order to do battle with Xoanon, the Doctor must escape, not only from the savage practices of the Sevateem but also from the mind-controlling impulses of the Tesh. 

The inhabitants of the planet Karfel are suffering under the tyrannical rule of their leader, the Borad, who has brought his world to the brink of interplanetary war. Those who dare to oppose the will of the Borad are mercilessly sacrificed to the Timelash, a fate considered by many to be worse than death. When the Doctor arrives on Karfel, he soon discovers the Borad's horrifying plan - and realises he must be stopped at all costs.

In 1890s Cardiff, reporter James MacFarlane is intrigued by rumours of ‘anaesthesia frolics’, at which gatherings the latest frontier in pain relief is demonstrated to influential guests. After he speaks to someone who attended several such ‘frolics’—and left with a hand and two fingers missing—James realises that the events have a dark side. Contriving an invitation, he is astounded to find another guest also investigating—it’s his old friend the Doctor! Reunited in mystery, the Doctor and James enter the murky underbelly of polite Cardiff society.

Geoffrey Beevers reads this exciting novelisation of a classic TV adventure for the Fourth Doctor. The Doctor is suddenly summoned to Gallifrey, the home of the Time Lords, where his ghastly hallucinations of the president’s assassination seem to turn into reality. When the Doctor is arrested for the murder, a hideous, dark, cowled figure is gleefully watching in the shadows. In a battle of minds, the Doctor faces renegade Time Lord the Master inside a nightmare world created by his old enemy’s imagination.

The TARDIS materialises on a remote island, set in a sea of acid, on the planet Marinus. The Doctor, Susan, Ian and Barbara meet Arbitan, keeper of a vast computer which rules and balances the gentle life of Marinus. Yet peace on the planet is threatened by the sub-human Voord, who wish to take control of the Conscience. Arbitan enlists the travellers to find the five crucial Keys of Marinus in various locations across the planet. Thus begins a series of terrifying adventures for the Doctor and his friends, who must find the Keys if they wish to ever to see the TARDIS again.