The TARDIS arrives on Earth in the middle of a meteorite shower and the Doctor is found by UNIT troops and taken to a nearby hospital. The Brigadier is faced with having to cope not only with the mysterious meteorites but also with Ransome, an ex-employee of a local plastics factory, who claims he has seen a walking mannequin.
The meteorites turn out to be hollow globes containing the Nestene consciousness, a disembodied alien intelligence with an affinity for plastic. A Nestene agent, Channing, has infiltrated the plastics factory and is using energy from the globes to animate Autons - mannequin-like figures and realistic replicas of senior establishment figures - with the aim of colonising the Earth.
Aided by newly-recruited UNIT scientist Dr Elizabeth Shaw, the Doctor thwarts this scheme by repelling the Nestene consciousness into space and thereby neutralising the Autons and the monstrous tentacled form that it has been creating for itself in a tank within the factory. Channing, revealed to be no more than a sophisticated Auton, is likewise deactivated.

It was noted for being the beginning of the end of the Doctor's exile on Earth, with the Doctor's TARDIS still under the control of the Time Lords (The Mutants) and restricted freedom (The Curse of Peladon and The Time Monster), as well as UNIT and the Master appearing less frequently in compared to the previous two series. As well as the return of the Daleks and the Ice Warriors, this series also introduced Alpha Centauri, Aggedor and the Silurians' aquatic cousins the Sea Devils.

William Hartnell returned in a cameo as the First Doctor and Patrick Troughton in a more substantial role as the Second Doctor in The Three Doctors. This story marked the end of the Doctor's exile on Earth, opening up the series to more off-world adventures and beginning a gradual reduction of UNIT-related stories.

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The TARDIS materialises in a hostile jungle on the planet Spiridon. Jo sets out alone to find help for the Doctor, who has fallen into a coma. She meets a party of Thals and is left in hiding aboard their crashed spaceship while they go to the Doctor's aid. The Time Lord, now recovered, learns of their mission to destroy a party of Daleks sent here to discover the native Spiridons' secret of invisibility.
Another Thal spaceship crash-lands in the jungle, and the survivors bring news that somewhere on Spiridon there is an army of ten thousand Daleks. Jo meanwhile meets a friendly Spiridon named Wester, who cures a deadly fungus disease that she has contracted.
It transpires that the Daleks' army is frozen in suspended animation in a cavern below their base. The Doctor, with the help of the Thals, explodes a bomb in the cavern wall and thereby causes one of the planet's natural ice volcanoes to erupt, entombing the army in a torrent of liquid ice.
The newly-arrived Dalek Supreme and his aides are left stranded on Spiridon as the Thals steal their ship and the Doctor and Jo depart in the TARDIS.

It was Jon Pertwee's final season as the Doctor and included, very briefly, the first appearance of Tom Baker as the Fourth Doctor. The Time Warrior, the season opener, introduced Sarah Jane Smith, who was a frequently featured character in the Doctor Who universe decades after her departure in Season 14. The same story also, for the first time, named the Doctor's homeworld as Gallifrey. UNIT also began to be phased out of the series during this season.

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The Doctor's past incarnations are taken out of time by a forbidden time scoop device. The fourth Doctor becomes trapped in the vortex but the others find themselves, together with a number of their old companions, with the fifth Doctor and his companions in the Death Zone on their home planet Gallifrey.
Here they face a Dalek, a Yeti, a quicksilver Raston Warrior Robot and numerous Cybermen. Also present is the Master, who has been summoned by the High Council of Time Lords to help the Doctor. It turns out that President Borusa is the mysterious operator of the time scoop. He aims to use the Doctors to breach the defences of the Dark Tower - Rassilon's tomb - so that he can enter there and claim immortality.
When he does so, however, he is condemned by Rassilon to eternal existence in the form of a living statue.

The Doctor is an observer and UNIT are providing security cover at an experimental drilling project designed to penetrate the Earth's crust and release a previously-untapped source of energy, named Stahlman's Gas after its discoverer. Professor Stahlman dismisses the concerns of the project's Executive Director Sir Keith Gold and exceeds all safety margins in order to expedite the work.
Soon however the drill head starts to leak an oily green liquid that transforms those who touch it into vicious primeval creatures with a craving for heat. The Doctor is accidentally transported by the partially-repaired TARDIS control console into a parallel universe where England is ruled by a military dictatorship.
The drilling project is at a more advanced stage here and, thwarted by his friends' ruthless alter egos, he is unable to prevent the penetration of the Earth's crust, which ultimately causes the planet's destruction. Escaping back to his own universe, where the drilling is still in progress, the Doctor tries to warn of impending disaster. At first he is disbelieved, but his words are borne out when the power-crazed Stahlman is himself transformed into one of the hideous primordial creatures.
The Doctor, aided by consultant Greg Sutton, kills Stahlman with ice-cold blasts from fire extinguishers. He is finally able to shut down the drilling with only moments to spare.

The TARDIS arrives in the year 2540 on board an Earth spaceship, which then comes under attack. The crew perceive the Doctor, Jo and the attackers as Draconians, whose empire currently rivals Earth's for control of the galaxy. The Doctor and Jo, however, see that the attackers are really Ogrons.
The Ogrons stun everyone on board and steal the ship's cargo - including the TARDIS. Accused by the Earth authorities of spying for the Draconians, the Doctor is sent to a penal colony on the Moon while Jo is placed in the custody of a Commissioner from Sirius 4 - actually the Master. The Master rescues the Doctor and locks him and Jo up aboard a stolen police spaceship.
Once in flight, the ship is intercepted by the Draconians. Taken to Draconia, the Doctor is able to convince the Emperor of the Master's scheme to provoke a war using the Ogrons and a hypnotic device that makes those affected see whatever they most fear.
Jo is recaptured by the Master and taken to the Ogrons' home planet, where he also has the Doctor's TARDIS. The Doctor follows with General Williams - an emissary from the President of Earth - and a Draconian Prince. Behind the Master's plot are the Daleks, who want a war to break out so that they can invade in the aftermath. The Doctor and his party are placed in the Master's custody as the Daleks leave to prepare their forces, but they manage to escape.
Williams and the Draconian Prince depart to warn their respective peoples of the Daleks' intentions. The Doctor, though, is injured in the confusion. Jo helps him into the TARDIS, where he sends a telepathic message to the Time Lords...

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The season introduces William Hartnell as the First Doctor, an alien who travels through time and space in his TARDIS, which appears to be a British police box on the outside. Carole Ann Ford is also introduced as the Doctor's granddaughter Susan Foreman, who acts as his companion alongside her schoolteachers Ian Chesterton and Barbara Wright, portrayed by William Russell and Jacqueline Hill, respectively. Throughout the season, the Doctor and his companions travel throughout history and into the future. Historical stories were intended to educate viewers about significant events in history, such as the Aztec civilisation and the French Revolution; futuristic episodes took a more subtle approach to educating viewers, such as the theme of pacifism with the Daleks.