"The Doctor Falls" is the twelfth and final episode of the tenth series of the British science fiction television series Doctor Who. It was written by Steven Moffat, directed by Rachel Talalay, and was broadcast on 1 July 2017 on BBC One. It is the second episode of a two-part story, the first part being "World Enough and Time". The episode received overwhelmingly positive reviews from television critics.
As a continuation of the previous episode, "The Doctor Falls" concludes the first televised multi-Master story of the show, as well as the origin of the Mondasian Cybermen. In the episode, the Doctor (Peter Capaldi) must save himself and the remaining human population of a gigantic colony ship from Mondas, while also dealing with two different incarnations of the Master (Michelle Gomez and John Simm) at once. The episode features a cameo from the First Doctor, now portrayed by David Bradley. He had previously played William Hartnell, the original First Doctor actor, in the 2013 Doctor Who docudrama An Adventure in Space and Time.
Plot
Aboard the colony ship reversing from the event horizon of a black hole, the Twelfth Doctor finds Bill has been converted into a Cyberman. The Master and Missy capture the Doctor, but he had earlier surreptitiously reprogrammed the Cybernet to target Time Lords as well, forcing them to flee. Nardole arrives in a commandeered shuttlecraft to rescue them. The Doctor is electrocuted by a Cyberman, but is saved by Bill.
They evacuate to a higher level of the ship containing a solar farm populated by children and a few adults fighting off early Cybermen prototypes. The Doctor recovers, but suppresses the early signs of regeneration. Bill initially remains unaware of her transformation, her strong mind acting like a perception filter, until one of the children inadvertently reveals the truth to her. Bill sheds a tear, which the Doctor calls a hopeful sign. Missy and the Master discover a camouflaged lift, a possible escape route. But when they call for it, an upgraded Cyberman arrives, which the group destroys. The Doctor warns that the time dilation affords the Cybermen more time to evolve and strategize.
Nardole discovers the floor directly below the solar farm contains fuel pipes. He is able to trigger controlled explosions, which are used to exaggerate the humans' defensive strength and defeat the Cybermen's initial attack. Knowing this ploy only delays their inevitable defeat, the Doctor instructs Nardole to lead the human community to a solar farm on another floor and remain there to safeguard them. Bill stays to fight with the Doctor. Despite the Doctor's impassioned plea, Missy and the Master abandon them, intending to take the lift to the lowest level and escape in the Master's TARDIS. Missy, however, changes her mind and stabs the Master, which will trigger his next regeneration. He retaliates by shooting her in the back with his laser screwdriver, telling her she will not regenerate. Both laugh over the irony of their mutual betrayal before the Master departs.
An army of Cybermen arrive, but are warded off by the Doctor until he falls after being shot. Surrounded, the Doctor ignites all the fuel pipes, engulfing the farm in a fireball and destroying or disabling the Cybermen. The Doctor lies still as Bill kneels beside him. She suddenly finds herself outside of her Cyberman body in her human form. Heather ("The Pilot") appears, having found Bill through her tears. She saves Bill by transforming her into an entity like herself. They leave the Doctor inside his TARDIS, and Heather invites Bill to explore the universe with her. Bill sheds tears for the Doctor before leaving with Heather.
The TARDIS arrives in a snowy landscape and the Doctor awakens, briefly dazed and confused, but then he starts regenerating. Refusing to keep continually changing, he emerges and seemingly stops his regeneration. Within, the cloister bell sounds an alarm as the Doctor encounters his original incarnation.
Continuity
Missy mentions that the Doctor once died in a fall, referring to events in Logopolis (1981), in which one of her previous incarnations causes the Fourth Doctor to fall from a radio telescope tower.
During the final battle, the Doctor lists the various sites of his encounters with Cybermen: Mondas (The Tenth Planet), Telos (The Tomb of the Cybermen), Planet 14 (The Invasion), Voga (Revenge of the Cybermen), Canary Wharf ("Doomsday"), and the Moon (The Moonbase). He also mentions Marinus, a reference to the events of Grant Morrison's Sixth Doctor comic The World Shapers, in which that planet's Voord evolve into Cybermen (though that story also suggests that Mondas, Planet 14, and Marinus are all the same planet).