In an apartment block in Britain, an old woman takes the lift. In the neighboring apartment, a young boy named George hears the sound and cowers in fear. His mother, Claire, hesitates on her way out and comes in to try and reassure him. She reminds her son that he needs to put the things that he's afraid of into the cupboard. He agrees but asks her to turn the lights on and off five times as part of their family ritual. Claire does so and tucks George in, but as she leaves George whispers for someone to save him from the monsters. He shines his torch around the room and watches as the shadows take on ominous forms. In the living room, Claire tells her husband, Alex, that George needs a doctor. Alex insists that they can handle it on their own.
The Doctor is navigating the TARDIS when he suddenly receives a telepathic message. He takes out his psychic paper and sees a message: "Please save me from the monsters." Informing his companions that he's going to make a house call, the Doctor sets course for the source of the signal. They arrive on earth and go into the apartment block.
In his bedroom, George listens to something making moaning noises in the darkness of his room. Outside, he hears the old woman walking by, pulling a handcart, and cowers at the noise. Outside, Alex looks at photos of his family together.
The Doctor, Amy, and Rory canvass the apartment trying to find the source of the message. The Doctor talks with an old woman, Mrs. Elsie Rossiter. Rory talks to the landlord, Purcell, while Amy deals with Julie and her creepy twin daughters. However, none of them find anything. As Amy and Rory walk by George's apartment, George peers out the window and the Doctor sees him from an adjoining balcony. As he heads for the apartment, Amy and Rory get into the lift and head down. However, it plummets out of control toward the ground. However, when it arrives, the door opens and there's no sign of the two companions.
The Doctor arrives at Alex's doorstep and the husband assumes that the newcomer is the doctor that Claire wanted to call in. He invites the Doctor in to examine George.
Mrs. Rossiter goes to the trash bin to leave off her garbage. As she goes back inside, she hears something moving among the bags and goes back to investigate. She assumes that it's George, but something grabs her and pulls her into the bags.
Alex tells the Doctor about George and how he has been a strange child ever since he was born. He had hoped that his son would grow out of it, but George is 8 and still afraid of everything. The Doctor assures him that he'll do whatever he can for George.
Amy and Rory find themselves in a shadowy room and Rory wonders if they're dead. Amy tells him to shut up and they start exploring, unaware that someone is watching them from the shadows.
The shadows in George's room continue to move on their own and object start coming to life. George screams and knocks over a lamp, and Alex runs in to help him. He figures that George was having a nightmare but the boy insists that he wasn't asleep. The Doctor comes in and tells George that he's there to help him with the monsters.
Rory and Amy find a kitchen but discover that the utensils are made out of wood. Amy picks up a "copper" pan as a weapon and opens a drawer. Inside is a giant eyeball, but the couple realizes that it's made out of glass. The lights start flickering and the couple continues looking for a way out.
The Doctor offers to put George's toys in the cupboard but the boy panics. Alex explains about the ritual where they put George's "fears" in the cupboard. The Doctor starts to open the cupboard but is interrupted when someone pounds on the front door.
Amy and Rory continue to explore while unseen figures stalk them from the shadows.
Alex goes to answer the door and greet Purcell, who is there with his dog, Bernard. The landlord demands the rent and tries to intimidate Alex into handing it over. Meanwhile, the Doctor scans George's room with his sonic screwdriver and then entertains the boy by using it to activate the boy's mechanical toys. However, when the Doctor scans the cupboard, he panics as he realizes that the readings are off the scale. While he checks the readings, George overhears Purcell threatening his father in the next room. Once Purcell leaves, Alex goes back to George's room and starts to open the cupboard door, but the Doctor stops him and says that his son's monsters are real.
Rory and Amy find the front hall but discover that the door to the outside has no door. Amy finds a grandfather clock with the hands painted on. They hear children laughing in the distance and someone walking through the house.
The Doctor makes tea while Alex complains that his visitor is feeding his son's fantasies. Alex tells the Doctor to leave but the Time Lord explains that he has old eyes and has seen things that Alex can't imagine. Now something has amplified George's mind, allowing him to somehow reach out to the TARDIS across time and space and call for help.
In the mystery house, Mrs. Rossiter is in a hallway and calling plaintively for help. Another of the shadow figures stalks her. Meanwhile, Amy and Rory try to find the source of the children's laughter and follow it to a closet. Inside they find a human-sized doll with a porcelain head. They assume it's a toy and leave... and behind them, the doll comes to life.
The Doctor glances at Alex's family photos and realizes that something is wrong with them, but can't work out what. He goes back and forth on whether to investigate the cupboard door and finally decides to open it.
Purcell is in his flat watching TV. He gets up to get a beer and the floor opens up beneath him, drawing him down. In a matter of seconds he disappears from sight as Bernard looks on.
The Doctor opens the cupboard but finds nothing inside except the typical children's toys, including a dollhouse. As he contemplates the cupboard, the Doctor realizes what is wrong with the photos. He brings them back and asks Alex what he remembers about the day George was born. Alex can't remember anything specific about the birth, but he finally remembers that Claire couldn't have children. The Doctor shows him the photos indicating that Claire was never pregnant any time before giving birth to George. He turns to George and asks what he is, and the cupboard starts to vibrate. The doors burst open and an unearthly force pulls them inside, while George chants for someone to save him from the monsters.
Purcell is in the mystery house and finds Amy and Rory. Before they can do anything, one of the human-sized dolls grabs Purcell. As they watch in horror, Purcell transforms into one of the dolls. The couple locks themselves in the library as the dolls come after them, chanting that they just want to play.
The Doctor and Alex find themselves in the mystery house and the Doctor realizes that they're inside the dollhouse. When Alex wonders how he could have ever believed that George was his son, the Doctor explains that there is a powerful perception filter at work, hanging everyone's memories. As they start exploring, another of the dolls follows them.
In the library, Rory barricades the door as the dolls try to break through.
As they explore the house, the Doctor and Alex hear the sound of the lift from the outside world. They find five electrical candles and watch as the lights flicker.
Amy tells Rory that all they can do now is open the door and fight their way past the dolls. He agrees and they try to run out. However, one of the dolls grabs Amy and transforms her into one of their own as Rory stares in horror.
Alex realizes that the five flickering lights are the same ritual that George uses to banish his fears. The Doctor congratulates him on working it out and explains that the cupboard has become a repository for George's psychic forces. One of the dolls attacks them and the Doctor discovers that his sonic screwdriver has no effect on them. He finds a giant pair of scissors and uses them to push the doll away, and then flees with Alex. As they go up the stairs, Alex takes the scissors and holds off the dolls as more of them arrive. The Doctor tells Alex that George is one of the Tenza, an alien race that spread throughout the universe by finding families to join. They use their telepathic abilities to convince the families that they were always their children. As the dolls close in and Rory comes down from the second floor, the Doctor tells Alex that George doesn't know what he's doing. He calls to George, telling him that he has to believe that he's safe.
In his bedroom, George finally faces his fears and opens the cupboard doors. The dolls surrounding the Doctor, Alex, and Rory go inert and George appears at the base of the stairs. However, when the dolls see their creator, they come back to life and advance on George. The Doctor realizes that George overheard Alex and Claire talking about sending him away, and that he believes his "parents" are ready to abandon him. He confronts Alex, who admits that his son isn't human. However, as the dolls prepare to kill George, Alex runs to him and embraces him, promising that he'll never send him away.
Everyone is restored to the real world with only vague memories of their transformation. When Claire returns home, she finds the Doctor making kippers for Alex and a much happier George. The Doctor assures Claire that everything is fine now and George is normal. As he goes, Alex worries that George may transform in the future, but the Doctor assures him that George will adapt normally now. The Doctor then leaves with Rory and Amy, while the memory of his coming death hangs over him.