In 1986 a new planet appears in the Solar System which turns out to be a long-lost twin of Earth's named Mondas. Its inhabitants are the Cybermen.

The Daleks are poised to spread the Dalek Factor throughout the history of Earth and begin by implanting the Doctor.

The TARDIS arrives on the Earth colony of Vulcan where the newly-regenerated Doctor assumes the identity of an Earth Examiner.

The Doctor's warnings are ignored and the Cybermen take over the base, hampering the crew's efforts to help Zeus IV.

With the Doctor out of action, it is up to Polly, Ben and Barclay to stop Cutler using the Z-Bomb and devastating half the world.

While the Doctor worries about the inert Daleks in the capsules, Lesterson makes plan to reactivate one of them.

The Doctor fails to convince the colonists of the danger posed by the Daleks and soon the other two are also reactivated.

With Bragen having taken over, the Daleks trick the rebels into turning them loose and only the Doctor can stop them wiping out the entire colony.

The Doctor discovers Polly and Ben aboard the TARDIS shortly before the ship arrives in 17th century Cornwall, where the local churchwarden gives the Doctor a cryptic message shortly before being murdered.

The Cybermen take over the base again, apparently to stop the humans using the Z-Bomb, but then the Doctor realises they intend to use it themselves to destroy Earth.

With Polly being held prisoner by the rebels, the Doctor and Ben decide to investigate them, while Lesterson discovers the Daleks are reproducing.

The Doctor is unable to convince the colonists that the Macra exist and an attempt to brainwash his companions results in Ben betraying his friends.

The Doctor and Polly manage to save Jamie from the Macra and then try to show the Pilot who is really in charge of the colony.

Trying to find the stolen TARDIS, the Second Doctor and Jamie are lured into a trap by the Doctor's old enemies the Daleks.

The Doctor and Jamie investigate Waterfield's antiques shop, where they are knocked unconscious and transported back to the 19th century.

With the experiment at an end, the Doctor begins to suspect the key to rescuing Jamie, Victoria and Kemel from the Daleks lies with Terrall.

The Doctor and Quinn attempt to escape in order to stop Bragen using the Daleks to take over the colony.

The TARDIS arrives at a holiday camp company with the crew worried by a prediction of giant crabs and the Doctor becomes interested in the apparent madman Medok's stories of creatures that roam the colony at night.

The Doctor, Polly and Jamie are sentenced to work in the pits and an escape attempt sees Ben's loyalties called into question again.

Pike is convinced that the Doctor knows the location of Avery's treasure while Polly and Ben try to convince the locals they were not responsible for Longfoot's murder.

Polly and Ben are placed in the custody of Blake, who reveals he also has his suspicions about the Squire, while the Doctor and Kewper are forced to team up to escape from Pike's ship.

The Doctor and his friends are at the mercy of Cherub, who is now seeking Avery's treasure for himself, while Pike prepares to attack the village.

The Doctor, Polly and Ben arrive in 1746, in the aftermath of the Battle of Culloden, and are captured by a group of Highlanders shortly before they themselves are captured by redcoats.

The TARDIS arrives on the Moon in the year 2070.When Jamie is injured, the other travellers are forced to seek the help of a moonbase afflicted with a space plague.

As part of the Daleks' experiment, the Doctor manipulates Jamie into attempting to rescue Victoria.