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The brilliant young physicist Henrik and his fellow students develop a fusion reactor that produces endless clean energy, potentially saving Earth from environmental catastrophe. The reactor, however, is harnessed for commercial use, and the consequences for the planet and society are devastating. By the year 2064, the world has been ravaged by climate change. The UN succeeds in developing a form of time travel that can return a person's memories and personality to the moment of birth. Henrik is sent back to the past in an attempt to prevent the escalation of a catastrophe before it is too late. Something goes wrong and Henrik is forced to begin his mission from a very different starting point to the one he is used to.

On the planet Xeros, the TARDIS crew discover their own future selves frozen in time as exhibits in a galactic museum and must avert this potential future.

Arriving in the town of Tombstone, the First Doctor finds himself involved with gunmen out to kill Doc Holliday...

The TARDIS has arrived on a far-distant and seemingly idyllic world. Yet the Doctor, Steven and Dodo learn it hides a terrible secret: the apparently civilised Elders maintain their advanced society by draining and transferring to themselves the life-force of the defenceless Savages.

The TARDIS arrives in London in 1966 and the First Doctor and Dodo visit the Post Office Tower. There they meet Professor Brett, whose revolutionary new computer WOTAN (Will Operating Thought ANalogue) can actually think for itself and is shortly to be linked up to other major computers around the world — a project overseen by civil servant Sir Charles Summer.

The TARDIS arrives on the coast of seventeenth century Cornwall — much to the astonishment of Polly and Ben. Pirates led by Captain Samuel Pike and his henchman Cherub are searching for a hidden treasure, while a smuggling ring masterminded by the local squire is trying to off-load contraband.

The time travellers arrive in Scotland just after the Battle of Culloden. The Second Doctor gains the trust of a small band of fleeing Jacobites by offering to tend to their wounded Laird, Colin McLaren. While Polly and the Laird's daughter, Kirsty, are away fetching water, he and the others are all captured by Redcoat troops commanded by Lieutenant Algernon Ffinch.

The TARDIS arrives on an extinct volcanic island. Before long, the travellers are captured and taken into the depths of the Earth, where they find a hidden civilisation — the lost city of Atlantis.

Time itself is in peril! The Time Lords and UNIT find themselves besieged by a mythic figure from the Time Lords' past hell-bent on destruction. The only way to defeat him is to break the First Law of Time and let the Doctor help himself — literally...

Picking up a distress call from the edge of the known universe, the Doctor and Sarah Jane find themselves on Zeta Minor where a geological team has run afoul of some strange goings on...

The TARDIS arrives in 2070 on the Moon, where a weather control station under the command of a man named Hobson is in the grip of a plague epidemic — in reality the result of an alien poison planted by the Cybermen. Jamie is knocked unconscious and lapses into a delirium, leaving the Second Doctor, Ben, and Polly to fight off a massive Cyberman attack.