In London in the year 2012, two posters about missing children are posted on a quiet suburban street. An elderly woman, Maeve, senses something amiss and her neighbor Trish Webber asks if she's okay. Maeve insists that that she feels something, but Trish insists she doesn't notice anything. Trish goes back inside as Maeve warns the neighbor children to go inside for safety. On the second floor of Trish's flat, a young girl watches everything that occurs. The girl, Chloe, sings to herself and watches the children as they play.
Chloe goes to the desk and draws a picture of one of the children, Tom, across the street, while Trish looks up the stairs in terror. Outside, a neighbor is ushering Maeve away when his son suddenly disappears. In Chloe's sketch, the image of Tom screams in silent terror.
The TARDIS arrives nearby and the Doctor and Rose come out. He explains that he's brought her to the year 2012 to see the Olympics, but Rose is more interested in the three missing person posters. The Doctor notices the unseasonal cold and they notice everyone on the street is scared. He runs off to the yard where the boy disappeared and reaches out to sense something. Meanwhile, a car abruptly stops on the street as its battery goes dead and a council worker, Kel comes over to check it out. Rose investigates while Kel says there's no reason for why cars stop from time to time. She helps push it down the street but it suddenly starts on its own. As the driver leaves, Rose confirms that it started happening the same time that the children went missing.
Tom's dad notices the Doctor on his yard and asks what he's up to. Meanwhile, Kel explains that he's been fixing the streets because the Olympic Torch will be run down the street. Maeve comes out and insists that the children disappear when they're playing. Once the Doctor confirms that he's a policeman, using his psychic paper, Trish comes out and asks what he plans to do. Tom's dad insists that the children are just running away, but Maeve warns that whatever is responsible is among them. Another neighbor accuses Kel of being the one responsible and they start arguing among themselves until the Doctor tells them to be quiet. He then confirms that three children have disappeared, and Maeve says that something evil has come to the street. Meanwhile, Chloe watches them from her window and Trish goes inside.
The Doctor starts sniffing around the neighborhood and notices the smell of burn fuses as he examines the locations where the children vanished. He figures whatever is responsible used a great deal of power.
Chloe looks down from her window and sees a cat, and starts sketching. Trish comes in and tells her she has to come down sometime, and then notices Chloe adding a cat to the sketch of Tom. When she asks her daughter why she drew Tom as sad, Chloe says she didn't draw him that way. She's drawing the cat that way so he'll have a friend. Trish brings up the TV broadcast about the Olympic Torch but Chloe isn't interested and continues drawing. Her mother insists that she's just having dreams and they can't hurt her, and Chloe threatens to draw her as well. Trish backs off and leaves, and Chloe finishes her sketch of the cat.
Rose notices that cat on the lawn and watches as it strolls into a box. A second later she hears a cat scream and checks the box, but the cat has disappeared. She shows the Doctor, who detects more energy residue. He says they need to find the source of the power and the person responsible.
In her room, Chloe tells the drawings to stop moaning since they're all together, and they're lucky they have each other while she's alone. Her pencil snaps and she makes a random scribble.
Rose goes off on her own to investigate and hears what appears to be the cat trapped in a garage. She opens the door and a mass of black lines attacks her. The Doctor attacks it with his sonic screwdriver and it contracts into a small ball and drops into Rose's hands. They take it to the TARDIS and confirm that it's graphite: pencil lead. The Doctor realizes whoever is taking the children and animals can also create things, and Rose realizes the scribble is a child's discarded drawing. She remembers that Trish was frightened of her daughter and figures Chloe is involved.
The Doctor and Rose go to the Cooper home and ask to see Chloe. Trish tells them to leave and the Doctor immediately marches off. Trish wonders why he wants to see her, and he explains that they thought Chloe might want to help them. They feign disinterest and leave Trish to deal with it on her own, and she asks if they can help her. The Doctor insists that he can and Trish invites them inside. Trish explains that Chloe stays in her room all the time and only asks to be left alone. Chloe's dad died a year ago, and Trish admits he wasn't a nice person. Trish goes to check on Chloe first, and the Doctor wonders why she's afraid of her daughter. The woman insists that Chloe is really a great kid, but now she's not herself.
Rose goes to the loo but then hides in the closet across from Chloe's room. When Chloe leaves, Rose goes into her room and sees all of Chloe's drawings taped to the walls, including the ones of the cat and the missing children. When something rattles the closet door, Rose jumps and knocks over some crayons. When she picks them up, she realizes that the people in the drawings have changed and are now snarling at her.
The Doctor finds Chloe in the kitchen and tries to talk to her. She insists that she's busy making something and that "they" don't stop moaning. She snaps at Trish when her mother tries to touch her.
Rose investigates the closet and finds a sketch on the wall, a figure of a large troll-like figure with glowing red eyes.
Chloe insists that she's busy and tries to leave, and the Doctor asks what she's making. Rose yells and he runs upstairs and slams the closet door shut. Chloe explains that she drew her dad because she dreams about him. She then says that she and someone else need to stay together, but she doesn't mean Trish. Trish orders Rose out, but the Doctor demands answers. They try to explain that Chloe has a power, but Trish refuses to accept it. The Doctor explains that she has to deny it because no one would believe her, but he tells Trish that he believes her.
Down in the kitchen, the Doctor explains that Chloe is using ionic energy to animate the drawings, including her father. He warns that Chloe's father is very close to entering the real world, and Rose wonders how Chloe has the power. They go to Chloe's room and the Doctor telepathically scans her mind. Chloe collapses and an alien voice speaks through her, saying it wants Chloe. The Doctor demands parlay in accordance with the Shadow Proclamation, but the entity doesn't care.
The entity finally admits that it's lonely and wants its friends, and it says that it was on an endless journey with its brothers and sisters, but now it's alone. It identifies itself as the Isolus and says its journey began in the deep realms. The Doctor explains that the Isolus Mother casts off millions of spores, but their empathic link sustains them. The entity says that they play games while they travel, creating imaginary worlds. It explains that its pod came too close when a solar flare scattered the pods. The other Isolus are in space, and the entity can't reach them. When it crashed on Earth, the pod was drawn to heat and the entity empathized with Chloe and entered her body. The Doctor says it can't steal any more friends. The drawing of her father animates in the closet and says that it's coming. The Doctor tells Trish to sing to her daughter to calm her down. Trish succeeds, quieting the creature in the closet.
They go downstairs and start putting away the writing supplies, and Trish admits that when her husband drank, he beat Chloe. Rose realizes that the Isolus will keep pulling people in, and that it has a family of four billion.
Upstairs, Chloe watches the countdown to the Olympics.
The Doctor and Rose go to the TARDIS to trace the Isolus pod's heat's signature, and that it's been absorbing heat so that it can launch.
As Trish calls a neighbor, Chloe slips out of the house. She watches as Rose and the Doctor enter the TARDIS. Inside the Doctor admits that he sympathizes with the Isolus, but Rose warns that kids can be terrors.
Chloe goes back to her room and takes hidden pencils out of a doll.
The Doctor says that they should try to understand the kids, and Rose is surprised to hear him admit that he had kids once. They detect the pod buried in the street. As they leave with some equipment, Chloe draws the TARDIS and the Doctor. As Rose walks along, she hears a crash and turns to see that the Doctor and the TARDIS have both disappeared. She runs up to Chloe's room and finds the Doctor's drawing. Rose demands that the entity bring the Doctor back, and he's the only one who can help it. It insists that it loves Chloe, and Rose understands. She goes outside to find the pod while on the TV, the torch bearer runs along the streets.
Rose sees Kel finishing his tarmac job and asks if there has been anything on the street that generates a lot of heat. She asks what happened six days ago and Kel remembers that he filled in the pothole the first time. Rose runs to his van and takes out an axe, breaks open the tarmac, and finds the pod.
Chloe finds more hidden pencils and starts drawing the Olympic stadium and everyone in it.
Rose comes inside and discovers that Trish has left her daughter. They look at the TV screen as the newscaster announces that everyone in the stadium has disappeared. Rose realizes that it won't be enough and the Isolus will seek out everyone on Earth.
Chloe/Isolus realizes that it's not enough, takes out a book with a picture of the Earth, and prepares to sketch after barring the door. Rose tries to tell it that’ she's found the pod, but the Isolus ignores her. While Rose hacks down the door with the axe, the voice in the closet says that it's coming. Rose breaks in, but the Isolus says that if Rose stops it, it'll release the creature in the closet. The Isolus insists that the pod is dead. The drawings begin to move and Rose sees the Doctor pointing to a torch in his drawing. Rose realizes what they need to charge the pod.
Rose runs outside as the Olympic Torchbearer comes down the street. The pod responds to it as it passes and Rose runs after the torchbearer. She tells it to feel the love and throws it into the air. It enters the flame, which bursts alight.
In Chloe's room, the Isolus realizes what happens, says it can go home, and leaves Chloe after saying it loves her. The creature flies out the window while Chloe runs into her mother's embrace.
All of the missing children reappear where they disappeared. There's no sign of the Doctor, and Rose realizes that all of the drawings have come to life. She runs to the house only to discover the doors have sealed themselves. The creature in the closet is coming down the stairs, yelling for Chloe. Rose tries to tell Chloe that it's not real, but it has form because they're scared of it. She tells Chloe to overcome her fear, but Chloe insists that she can't and calls for her mother. Trish says that Chloe isn't alone and never will be again. Rose tries to get in and yells at Chloe to sing. Mother and daughter sing and the creature retreats, screaming in frustration.
Kel comes over to reassure Rose, but she wonders who will accompany the Doctor now. She goes inside and they watch as all of the stadium spectators reappear. They watch as the Torchbearer arrives in the stadium but collapses. However, the Doctor arrives, picks up the torch, and bears it to the great flame. He sets it afire and tells the Isolus to go to its brothers and sisters. It lifts up into the air as the crowd cheers.
The Doctor returns to the street and Rose offers him a piece of cake. They hug and the Doctor insists that it's a night for lost things to be found. As they go to watch the games, the Doctor tells her some spoilers but she's not sure if he's joking or serious. As they leave, Rose says that they'll always be together. The Doctor isn't so sure, and says that he senses a storm approaching.