Phoebe and Piper notice a cute guy checking out Piper. Prue has a tune stuck in her head and asks Piper and Phoebe if they recognize it. They don't. Justin ("Coyote Piper") has asked the sisters to come to a barbecue. Meanwhile, an ice cream truck trawls the streets, playing that same tune, an odd sight at night; a boy walks up and a man in the truck offers him some ice cream. A strong wind pulls the boy into the truck.
Prue sleeps fitfully and dreams of herself as a child in a snow-covered playground. She screams for help and her father rescues her just as the alarm clock sounds. Phoebe is at her laptop and gets an instant message from "an old friend", but is unwilling to share with Prue. Piper reports that a longtime friend saw their father in the Bay Tech Building and wants to ask after him. She asks Prue to go along, but Prue has a photo shoot on Nob Hill.
Prue is riding in an elevator when she hears a little girl singing the same tune that's been stuck in her head. The elevator stops, but Prue can't get out in time to ask the girl about the tune. Piper asks after her father at the Bay Tech Building, but he is not there. She thinks she sees him, but is mistaken.
Prue and Phoebe hear a girl humming the tune stuck in Prue's head. The girl points to the ice cream truck as it passes. The girl runs toward the truck. Prue gets suspicious, since it's the middle of winter. She and Phoebe run after the girl and find her being drawn into the truck; they try to rescue her, but are pulled in with her instead. The two find themselves in the snow-covered playground of Prue's dream. The Ice Cream Man asks who they are, but then flees. A boy, Ari, warns the sisters about the Nothing, and warns them to get away before they get pulled in. He leads them to a hiding place. The girl runs out, but then the Nothing takes her.
Piper notices that Prue and Phoebe are missing. A young man enters P3 and introduces himself as Caleb, and Piper has to reject him clumsily.
Ari tells Prue and Phoebe that he and others pulled into the truck have been on the run from the Nothing. Phoebe has a vision of Prue's experience in the ice cream truck. She had been in the same playground and rescued by their father.
Piper calls for Leo, but he can't sense Prue and Phoebe.
Prue and Phoebe gather Ari and two other surviving children-- a girl, Freckles, and another boy, Jersey. The ice cream man skulks nearby and the sisters try to follow him. He runs off into the woods. Phoebe sees a portal on top of the slide, leading out to the street. Prue and Phoebe lead the children through the portal as the ice cream man urges them not to, and then escape themselves. The ice cream man tries to follow, and tries to pull Ari back into the truck. However, Ari grabs the ice cream man's wrists and burns them severely before shoving him back into the truck. Realizing that Ari is a Demon, Prue and Phoebe are horrified. They want to get Freckles and Jersey away from Ari, but Ari tells them they won't listen to them. The three children thank the sisters and run off laughing.
Piper is very worried about Prue and Phoebe, and calls for Leo. He can't sense them, but reassures her that they're okay. Just then, Prue and Phoebe come in. Phoebe tells them that they thought they were rescuing innocent children, but they were really demons, and the ice cream man was the real innocent. They consult the Book of Shadows. The ice cream man turns out to be a mortal who catches demon children with his ice cream truck. The truck plays a song called "the Devil's Chord," which attracts the children to the truck, where they are sucked in. Prue realizes this was the same tune she'd had stuck in her head earlier. The Nothing can then vanquish them, but it does not distinguish good from evil. They need a mortal to open the truck so they can somehow save the ice cream man. Prue tells of Phoebe's vision. Phoebe confesses that Victor has been in town for three months; the instant message from "an old friend" was from him.
Jersey stands over over a charred corpse. Ari walks up with Freckles and asks what was going on. Jersey tells him that the corpse is an ice cream man that he just burned alive. Freckles is excited, but Ari is furious. Ari wants to kill, but doesn't want to keep indiscriminately killing ice cream men in order to get the truck they want. However, he's willing to kill the sisters in order to get to him. Freckles blows on her hand in the direction of the corpse, and it disappears.
Phoebe gets in touch with Victor and arranges for them all to meet at P3. While the sisters are waiting for him, Caleb arrives and Piper tries to make him go away. Just then, Leo comes in behind him. Piper begs for help, and Leo tells Caleb he has a phone call and they leave. Victor enters and the sisters ask about the playground. Victor doesn't cooperate at first, but then tells of his experience. Victor was staying home with Prue when she had a cold. Prue had come down and heard the ice cream truck. She saw a boy pulled into the truck and gone after her. He entered the truck and rescued Prue. Grams was furious with him, and that was when Victor left for good.
The Halliwells go looking for the truck, but find it missing. Just then, they hear laughing behind them. The demon children sneak up behind them. Freckles blows the Halliwells into some trash. The demon children run off, much to the Halliwells' surprise. Piper and Phoebe go after the demon children while Victor and Prue break into the impound lot. After Prue makes one final attempt to pop open the door, Victor opens the truck and he and Prue enter. They try to rescue the ice cream man. He tells them that he knew all along that Prue, Piper and Phoebe were the Charmed Ones; the Elders had alerted him when Prue and Phoebe accidentally got pulled in. He has no hard feelings; anyone would think that children were automatically innocents. He gives Prue a part that he removed from the truck; it plays the Devil's Chord. As the Nothing approaches, the ice cream man sacrifices himself so Prue and Victor can escape. Piper and Phoebe spy on the demon children. They overhear Ari telling Jersey and Freckles that they can destroy the truck so they can't be captured again. This explains why they didn't really want to fight the sisters. Piper isn't concerned; it's three against three. Just then, three more demon children show up. Piper and Phoebe head to the impound lot, not knowing the demon children followed them. While Piper and Phoebe are waiting for Prue and Victor, they hear the demon children's laughter. A demon child throws an object at Piper, knocking her out. Meanwhile, inside the truck, Victor and Prue climb toward the exit. The Nothing tries to take Prue, but Victor grabs hold of her.
The demon children surround Phoebe. One of them jumps on Phoebe's back, but Phoebe throws him over her shoulder and into Freckles. Freckles recovers and blows Phoebe into the wall. Just then, Prue and Victor come out of the truck, and Prue sends the demon children flying in all directions. Freckles gets up and is about to blow Prue off her feet, but Prue gives her a "time-out" by swatting her into the fence. Jersey throws fire at Prue and Phoebe, forcing them behind a car. Victor is trying to figure out where the part goes when Ari creeps up behind him. He starts to use his burning power on Victor, but Prue sends him flying. Victor re-installs the part. The demon children, as if in a trance, walk toward the truck and are sucked in.
As Piper comes to, Leo enters with Caleb. Caleb turns out to be the new ice cream man.
Victor is now reconciled with his daughters. He has a job interview and if he gets the job, he'll be based in San Francisco.