Clara (Jenna Coleman), on a date with Danny Pink (Samuel Anderson), gets into an argument about his career as a soldier. Returning to her flat, she finds the Doctor (Peter Capaldi), who wants her help tracking down a creature with the perfect ability to hide, which he believes inspires everyone’s childhood fear of a hand grabbing them from under the bed.

Clara uses the telepathic circuits of the TARDIS to take her back to her childhood, but her thoughts wander, and she ends up in Danny’s childhood home. He was called Rupert then (Remi Gooding), and is frightened by something under his bedspread. The Doctor suggests he use his fear to gain power and Clara suggests he protect himself with toy soldiers. Comforted, he falls asleep and the Doctor scrambles his memory, giving him dreams of being a soldier.

Back in the present, Clara apologises to Danny, but her familiarity with his past disturbs him, and he leaves. She is brought back to the TARDIS by a space-suited figure named Orson Pink, who has a toy soldier heirloom. The Doctor had found him with the telepathic circuits--one of the first time-travel pilots from Earth, trapped at the end of the universe. An air seal ruptures, and the Doctor loses consciousness. Orson rescues him.

Clara uses the telepathic circuits to return by herself in the TARDIS, ending up in a barn, where a boy is sleeping fitfully. Clara hides under his bed when two adults enter, complaining that the boy is not fit to be a Time Lord. She realizes it is the Doctor as a child. After the adults leave, she hears the present Doctor’s voice coming from the TARDIS and the child tries to get out of bed. Afraid of him coming into contact with himself, she grabs his ankle. She realizes that she created that fear in him, repeats the adult Doctor’s advice, and the child falls asleep. Back in the TARDIS, when the Doctor awakes, she makes him promise never to investigate. Orson and Clara are dropped off when they belong, and Clara and Danny apologise with a kiss.

The barn that the Doctor as a child liked to hide in was the place on Gallifrey where the War Doctor engaged The Moment, which ended the Time War. Several lines by previous Doctors are repeated in the script. Clara quotes a line from An Unearthly Child: “Fear makes companions of us all.” The young Doctor was modelled after a photo of William Hartnell as a child. The episode received critical acclaim for its creepiness and its depth. It was nominated for a Bram Stoker Award and the Hugo in 2015.