Still following the Black Guardian's orders, Turlough sabotages the TARDIS.

The TARDIS is temporarily captured by the Mandragora Helix, a spiral of energy with a controlling influence, at the centre of which the ship is infiltrated by a sparkling ball of energy.

The Daleks control humans.

The Dalek Invasion of Earth: The Daleks (30m)

As plague sweeps the country, the Doctor discovers a more exotic threat at work - shipwrecked Terileptil convicts, intent on making the planet their own.

The planet of Tara holds the fourth segment of the Key as a statue, and the Doctor becomes involved in the feud that exists between Count Grendel and Prince Reynart.

When the TARDIS lands in the swamp lands, the monstrous Kroll, who swallowed the fifth segment centuries before, rises from the depths. In order to revert Kroll to its natural form, the Doctor must get the key tracer near him before it's too late.

The Doctor and company drop in on a planet in the midst of an interplanetary war.