The Doctor, Sarah and Harry return to Earth in response to the Brigadier's summons. UNIT are investigating a series of attacks on North Sea oil rigs and have set up a temporary HQ in the Scottish village of Tullock. The attacks are the work of a huge cyborg, the Skarasen, controlled by a group of aliens called Zygons whose spaceship lies at the bottom of Loch Ness.

The time ring takes the Doctor, Sarah and Harry back to Nerva, but to a period many thousands of years earlier than their previous visit. The station is currently acting as a beacon warning space traffic of the existence of a new asteroid orbiting Jupiter.

The Doctor and Romana visit the Leisure Hive on the planet Argolis, the surface of which is uninhabitable following a twenty minute nuclear war between the Argolins and their enemies the Foamasi. The Argolins themselves are now sterile. Pangol, the youngest, was created by the Tachyon Recreation Generator, a machine that runs games in the Hive.

Conclusion. The Doctor races to destroy the parasite in the mind-control machine and thwart the Master's escape plans.

The Doctor meets the most important woman of his life.

Agatha Christie's 10-day disappearance in 1926 may have been the result of amnesia, a nervous breakdown, or a giant alien wasp.

Part 1. The Doctor and Donna must uncover the truth behind the Nodes and the Data Ghost to uncover the library's secret.

Part 2 . As the shadows rise, the Doctor forges an alliance with the mysterious River Song.

The Doctor is trapped, powerless and terrified, on the planet Midnight, as a knocking on the wall begins.

Donna gets help from a mysterious blond woman.

Part 1. Earth's greatest heroes assemble to fight the New Dalek Empire, but a fearsome old enemy waits in the shadows.

Part 2. As Davros and the Daleks threaten the entire universe, the Doctor's companions join forces. However, the prophecy declares that one of them will die.

An eight-million-year-old skull is the subject of experiments. Tom Baker, Louise Jameson. Colby: Edward Arthur. Thea: Wanda Ventham. Stael: Scott Fredericks. Hiker: Graham Simpson. Fendelman: Denis Lill.

Witchcraft and strange creatures add to the mystery at the priory. Tom Baker, Louise Jameson. Ted Moss: Edward Evans. Jack Tyler: Geoffrey Hinsliff. Thea: Wanda Ventham. Adam Colby: Edward Arthur. Mitchell: Derek Martin.

The Fendahl gains power by absorbing the life force of humans. Tom Baker, Louise Jameson. Adam Colby: Edward Arthur. Fendelman: Denis Lill. Thea: Wanda Ventham.

The Doctor employs ancient powers to overcome the Fendahl. Louise Jameson. Jack Tyler: Geoffrey Hinsliff. Martha: Daphne Heard. Thea: Wanda Ventham. Adam Colby: Edward Arthur. Ted Moss: Edward Evans.