A lonely doctor who once occupied an unusual lakeside home begins exchanging love letters with its former resident, a frustrated architect. They must try to unravel the mystery behind their extraordinary romance before it's too late.
The Doctor, Jamie and Zoe arrive on an unnamed planet. At first believing themselves in the midst of World War I, they realise it to be one of many War Zones overseen by the War Lords, who have kidnapped large numbers of human soldiers to form the greatest army the universe has ever seen. At the helm of this plot is the War Chief, another renegade Time Lord like the Doctor. The creeping realisation sets in that the Doctor cannot solve this problem alone, and that his days of wandering may be at an end...
Professor Emil Keller has created a machine that can pacify even the most dangerous of criminals. But when the Doctor and Jo arrive at Stangmoor Prison for a demonstration, things start to go horribly wrong - especially when they discover that the Doctor's old enemy the Master is responsible for the machine.
A group of gold-skinned aliens known as the Axons land on Earth and offer wondrous technology in exchange for fuel. The Doctor, however, isn't fooled, uncovering the Axons' true nature and once again facing his archenemy the Master...
When the Master steals the Time Lords' secret file on the Doomsday Weapon, they grant the Doctor a temporary reprieve from his exile on Earth to deal with the crisis. He and Jo arrive on the planet Uxarieus and become enmeshed in a struggle between an agrarian colony and a powerful mining corporation.
On the eve of May Day, dark elemental forces begin to disturb the village of Devil's End as the Master summons the demon Azal: unexplained murders, a stone gargoyle come to life, and a nigh-impenetrable infernal energy dome. With the Master fully prepared to destroy the Earth, the Doctor and UNIT - aided by a benevolent practitioner of witchcraft - battle the wicked rites of a secret science wielded by an alien from another world.
The TARDIS arrives on the unnamed planet of the Gonds, who are ruled and taught in a form of self-perpetuating slavery by the alien Krotons — crystalline beings whose ship, the Dynatrope, crash-landed there thousands of years earlier after being damaged in a space battle. The Krotons are in suspended animation, in a crystalline slurry form, awaiting a time when they can be reconstituted by absorption of mental energy. Periodically, the two most brilliant Gond students are received into the Dynatrope, nominally to become "companions of the Krotons", but in truth to have their mental energy drained, after which they are killed.
The TARDIS materialises in Earth's future on a space beacon just before it is attacked by pirates. The travellers find themselves trapped in a sealed section of the beacon. It is blown apart and flown to where the pirates will plunder it of the precious mineral argonite. They witness a conflict between the pirates and the Interstellar Space Corps, led by General Hermack and Major Warne. The ISC are convinced that the pirates' mastermind is an innocent yet eccentric space mining pioneer named Milo Clancey, while their true leader is a man named Caven. Caven has a secret base on the planet Ta. He is assisted by Madeleine Issigri, daughter of Clancey's ex-partner Dom, who - unknown to her - is now his captive. When Madeleine discovers Caven's full treachery, she helps to bring him to justice. The time travellers are given a lift back to the TARDIS by Clancey in his rickety old ship, the LIZ 79.
Peggy Sue faints at a high school reunion. When she wakes up she finds herself in her own past, just before she finished school.
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 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 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 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.