Kris and Lindy Powell are twelve-year-old identical twins who share a bedroom and constantly compete with each other. Lindy wears her blond hair long while Kris keeps hers short, one of the few ways to tell them apart. One spring afternoon, while exploring a house under construction next door, Lindy rummages through a Dumpster and pulls out a ventriloquist's dummy: a grinning figure in a gray suit with painted brown hair and blue eyes. She names him Slappy, improvises a squeaky voice, and begins making Slappy insult Kris. Neighborhood children are delighted by the performance, while Kris sits on the curb, dejected.
Over the following week, Lindy rehearses daily with Slappy and brings him to school, where classmates respond enthusiastically. A neighbor hires Lindy to perform at a birthday party for twenty dollars. That evening, Kris asks for a dummy of her own. Lindy protests, calling Kris a copycat, and their parents suggest the girls share Slappy. When Lindy resists, Slappy suddenly snarls insults at Kris and slaps her across the face. Mr. Powell demands Lindy apologize, and she reluctantly hands the dummy over.
Mr. Powell soon discovers a second ventriloquist's dummy at a pawnshop near his office and brings it home for Kris. The new dummy has bright red painted hair and wears jeans, a flannel shirt, and high-top sneakers. Kris names him Mr. Wood and begins practicing, with her friend Cody Matthews, a quiet boy from the neighborhood, as her audience.
Strange things begin happening. The next morning, Mr. Wood has moved from his chair and is propped against the bedroom doorway, dressed in Kris's skirt and blouse, the outfit she had laid out for a school event. Kris accuses Lindy, but Lindy insists she slept through the night. That Saturday, while Kris practices in front of friends, Lindy takes Mr. Wood to demonstrate a technique. The dummy suddenly snarls crude insults at Kris in a harsh, growling voice. Lindy claims she is not controlling the dummy, that Mr. Wood is speaking for himself. Lindy hands Mr. Wood back and hurries off to perform at a birthday party.
Lindy's success grows. She returns from the party having earned twenty-five dollars and reports she has been booked for another performance. Kris shares her own good news: Mrs. Berman, the school music teacher, has asked Kris and Mr. Wood to host the upcoming spring concert. The disturbances escalate. That night, the girls find Mr. Wood sprawled on top of Slappy with his hands wrapped around Slappy's throat. Both deny responsibility. Their mother dismisses their concerns and threatens to confiscate both dummies. Kris shuts Mr. Wood in the closet before bed, but by morning he has returned to the chair. Later, Kris goes downstairs and discovers the kitchen in chaos: the refrigerator emptied onto the floor and Mr. Wood sitting upright amid the mess. Mrs. Powell is furious and gives the girls one final chance.
Back in bed, Kris hears a muffled voice from the closet shrieking to be let out. Then Lindy confesses. She has been behind every disturbing incident: moving Mr. Wood at night, dressing him in Kris's clothes, making him speak the insults, arranging the violent tableau, trashing the kitchen, and throwing her voice to mimic the dummy calling from the closet. Lindy explains she did it all to scare Kris, angry that her sister copied her by getting a dummy. The whole thing was a prolonged practical joke. Kris is furious and humiliated for having believed the dummy was alive.
Days later, while practicing alone with Mr. Wood, Kris notices a folded yellow sheet of paper in his shirt pocket. It contains a single sentence in an unrecognizable language: "Karru marri odonna loma molonu karrano" (80). Kris reads the words aloud. Mr. Wood appears to blink, but she dismisses it as paranoia.
That evening, Mr. Powell asks both girls to perform for the Millers, an elderly couple from next door. Lindy goes first with Slappy and earns applause. When Kris takes her turn, Mr. Wood launches into vicious insults in a raspy voice Kris is not producing. Her parents are appalled, and no one believes Kris's protests. They ground her for two weeks. At the spring concert the following night, Mr. Wood takes the microphone as master of ceremonies and hurls cruel insults at Mrs. Berman, then tilts his head back and spews putrid green liquid over the front rows. The auditorium erupts in chaos. At home, Mr. Powell orders Kris to shut Mr. Wood in the closet and announces he will return the dummy to the pawnshop on Monday.
That night, unable to sleep, Kris hears footsteps from the closet. She follows a figure to the stairway landing and finds herself face-to-face with Mr. Wood, walking on his own. He giggles and declares in a growling voice that he is alive. Kris wrestles with the dummy on the stairs. He is surprisingly strong and punches her in the stomach. Lindy wakes and runs to get their parents, but by the time they arrive, Mr. Wood lies motionless on the carpet. The parents return to bed, convinced Kris is imagining things.
Once they leave, Mr. Wood springs back to life. He tells Kris she brought him back by reading the ancient words and declares both sisters must serve as his slaves, threatening to harm their loved ones if they refuse. Kris reads the incantation again, hoping to reverse the spell, but Mr. Wood laughs: The words only bring him to life and cannot destroy him. The girls try to pull his head off and cut it with scissors, but nothing works. They wrestle him into an old suitcase and shove it into the closet.
At three-thirty in the morning, the girls sneak the suitcase to the construction lot next door and bury it with Mr. Wood still screaming inside. They fall asleep believing the ordeal is over, but the next morning Kris finds Mr. Wood seated at the kitchen counter, his face smeared with dirt, grinning. When their parents leave to go shopping, Mr. Wood drops to the floor and seizes Barky, the family's small black terrier, by the throat. The girls tackle him and pry the dog free.
They carry the struggling dummy toward the construction lot, intending to throw him under one of the steamrollers. Barky escapes from the house and runs into the path of a machine. Both girls release Mr. Wood and dive toward the dog, who scampers away safely. Mr. Wood breaks free and raises his hands in triumph, but before he can run, the second steamroller rolls over him with a loud crunch. A cloud of foul-smelling green gas erupts from beneath the wheel. The girls assure the alarmed operator it was only a dummy.
Relieved, the girls return to their bedroom. As Kris leans over to close the window, Slappy, who has been sitting silently in the chair throughout the story, reaches up and grabs her arm. In a throaty growl, he asks, "Hey, slave — is that other guy gone? I thought he'd never leave!" (132). A second living dummy has been waiting all along.