A three-man rocket crew are nearly done with their mission to Titan Base until a course change puts the rocket in the path of a strange cloud in space. By the time they arrive, they have come under the control of a sentient virus which threatens the galaxy. When the TARDIS picks up an emergency message, it flies into the cloud, infecting the Doctor. To save himself and others, he must undertake a dangerous journey.
Far in the distant future, Earth has become uninhabitable, forcing Mankind to colonise first Mars and then Pluto. No longer the coldest planet in the solar system, Pluto is now warmed by artificial suns. The Doctor, Leela and K9 arrive to discover the exploitation of the Megropolis people by the ruling elite, lead by the Collector. Deep in the Undercity, a small group of revolutionaries plot to overthrow the company and the Doctor is forced to fight the oppression of the people using Fire against Fire...
On the edge of the universe, the Doctor, Leela and K9 encounter a Minyan ship on an epic quest to find their race banks... but their people have encountered the Time Lords before...
The Doctor returns to Gallifrey, claims his rights and is inaugurated President. It soon turns out that he has led a group of aliens called Vardans to the planet to eradicate them completely. After they are destroyed, the Sontarans take their opportunity and follow them in their invasion until they are destroyed by the Doctor.
The Doctor and Romana learn the second segment of the Key to Time is on the planet Calufrax. Yet they arrive on a planet called Zanak, which has been hollowed out and fitted with hyperspace engines, allowing its insane, half-robot Captain to materialise it around smaller planets and plunder their resources.
Searching for the third segment to the Key to Time brings the Doctor and Romana to present-day Earth, where the travellers have to contend with stone circles, Druidic rituals and a not-so-mythical goddess known as the Cailleach.
The Doctor needs somewhere peaceful to recover from his traumatic regeneration. But the sanctuary of Castrovalva is not all it seems, as the Master will stop at nothing to gain his revenge over the Doctor...
The Doctor and his companions arrive on a spaceship headed for Earth, populated by natives of Earth from various different eras and commanded by the leaders of the Urbankan race. What are the Urbankans' intentions when they reach Earth?
The Doctor and his companions are pursued through time and space by the Daleks on the desert planet Aridius and beyond.
In England, 1066, the Doctor confronts a mysterious Monk who is attempting to change history.
The Doctor, Vicki and Steven arrive on an arid planet where they meet the beautiful Drahvins and the hideous Rills. Each has crash-landed after a confrontation in space. The Rills are friendly, compassionate explorers. The Drahvins are dull-witted, cloned soldiers, terrorised by the intelligent, warlike matriarch Maaga.
When the TARDIS arrives on the plains of Asia Minor not far from the besieged city of Troy, the Doctor is hailed by Achilles as the mighty god Zeus and taken to the Greek camp. He meets Agamemnon and Odysseus. Forced to admit he is a mere mortal — albeit a traveller in space and time — he is given two days to devise a scheme to capture Troy. Steven and Vicki, meanwhile, have been taken prisoner by the Trojans. Vicki, believed to possess supernatural powers, is given two days to banish the Greeks to prove she is not a spy.
In the year 4000, the Daleks conspire to conquer the Solar System. Their scheme involves treachery at the highest levels and a weapon capable of destroying the very fabric of time. Only the Doctor and his friends can prevent catastrophe — and there is no guarantee they will escape with their lives...
The TARDIS materialises in Paris in the year 1572 and the Doctor decides to visit the famous apothecary Charles Preslin. Steven, meanwhile, is befriended by a group of Huguenots from the household of the Protestant Admiral de Coligny. Having rescued a young serving girl, Anne Chaplet, from some pursuing guards, the Huguenots gain their first inkling of a heinous plan being hatched at the command of the Catholic Queen Mother, Catherine de Medici.
The Doctor and his companions Steven Taylor and Dodo Chaplet arrive some ten million years into the future, on board a generation starship which is carrying the last of humanity away from an Earth that is about to fall into the Sun. However, the cold that Dodo has could prove devastating to these future humans and their servants, the Monoids.
The travellers arrive in a strange domain presided over by the Celestial Toymaker — an enigmatic, immortal entity who forces them to play a series of games, failure at which will render them his playthings for all eternity.
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.