Tahira

The Doctor uses the TARDIS to drop off her three travelling companions, Graham O'Brien, Ryan Sinclair and Yasmin Khan, back home in Sheffield for a few hours so that they can catch up with family and friends. However, shortly after arriving Graham gets a vision of a trapped woman asking for his help, while Yasmin, along with Ryan's friend Tibo, have nightmares and awake to see a dark-clothed man in their rooms. Ryan witnesses the man's fingers detaching and inserting themselves into Tibo's ear before vanishing with Tibo.

Meanwhile, The Doctor, alone in the TARDIS, receives an alert from 1380 in Aleppo, Syria. There she finds a woman called Tahira being terrorised by a threatening creature that has taken everyone else in the hospital.

After The Doctor's companions call her simultaneously to tell her what has happened to them, she takes them all to the near-colliding planets from Graham's vision using the TARDIS' telepathic circuits.

The Doctor

They land on a spaceship near the planets where they find a small prison structure keeping the planets from actually colliding. The Doctor discovers that the spaceship houses a power source, guarded by a quantum fluctuation lock, that powers the prison and is sending it a signal from the man's fingers.

Tahira and The Doctor’s companions wander off on the spaceship and are captured by the man, trapping them in their nightmares. Yasmin’s nightmare sees a younger version of herself having run off and on a lonely road. Ryan’s nightmare is about an Earth surrounded by flames and the Dregs (that he encountered in "Orphan 55"). While Graham’s nightmare has him waking up in a hospital where he sees his late wife, Grace, as a nurse who tells him that his cancer has returned.

Yasmin

The Doctor manages to open the lock just as the man confronts The Doctor and introduces himself as Zellin, an immortal god. Zellin reveals that it was his plan to use the captured humans to lure The Doctor there and trick her into opening the lock.

The prisoner is actually another immortal god, Rakaya. Zellin had been transmitting the captured humans' nightmares to keep Rakaya sane. The two gods take delight in seeding chaos in mortal beings which led to those on the near-colliding planets to turn against them and imprison Rakaya.

The Doctor is imprisoned as the gods arrive on Earth to feed off humanity's nightmares, but The Doctor manages to escape and free the others. Able to control Zellin's detached fingers, she also realises that the creature in Aleppo stemmed from Tahira's own nightmares and consequently cannot attack her. The Doctor lures the gods to Aleppo with the help of the creature. Using Zellin's fingers, she traps them all in the prison.

The Doctor is Attacked

Afterward, it is revealed that three years before her travels with The Doctor began, Yasmin was contemplating suicide as she was getting bullied and had low grades at the time. She was stopped by a police officer that Yasmin’s sister Sonya called. The police officer bet Yasmin 50p that her life would get better, claiming she would give Yasmin £50 if it does not. In the present, Yasmin visits ex-police officer Anita Patel to give her back the 50p. She invites Yasmin into her house and they reminisce.

Back in the TARDIS, Graham is confiding in The Doctor about his cancer scares and Ryan talks to Yasmin about being unsure about continuing travelling with The Doctor as he is worrying about missing parts of his friends' lives and not being there for them.

Possible sensing something is up The Doctor declares that they are going to visit Mary Shelley as she operates the TARDIS controls.