Lake Manitoc, Wisconsin
Sophie Carlton goes for a morning swim in the nearby lake. She swims for some time, going a considerable distance from shore. Suddenly she is dragged under water and never surfaces...
A week later, Dean finds the article on Sophie, whose body was never recovered. There have been two other drownings in the last year, and in each case the body was never recovered. Sam objects, saying it has nothing to do with their father, but Dean insists that until they do find something on John, they're going to kill every monster they can find. The brothers drive to Lake Manitoc and introduce themselves as Agents Ford and Hamill of the Fish and Wildlife Service, They talk to Will Carlton, Sophie’s brother, and he insists that Sophie was a varsity swimmer and wouldn't have drowned, so something must have attacked her. When they ask to talk to Bill Carlton, Sophie’s father, Will says that he didn't see anything and he's too upset to talk.
Next, the Winchesters talk to Sheriff Jake Devins, who says that the lake hosts no large carnivorous animals. Devins suggests that the stressful situation might have caused Will to see something that wasn’t there, and they checked the lake with sonar and dragging to make sure no animals could have killed her. He can't explain why they haven't found Sophie's body, or the other two victims. The sheriff mentions that it won't be a problem in six months, and explains that the dam that creates the lake has fallen into disrepair. The Federal government won't pay for the repairs, so they've opened the floodgates. In a few months the lake will be gone. Devins' daughter Andrea and her young son Lucas come in. Lucas is too shy to talk to them, and Devins says that he's been through a lot. Dean asks Andrea to walk them to a decent motel, and she agrees. As they walk, Dean talks about how he loves children. When Andrea drops them off, she notes that she isn't impressed with Dean's attempt at a pickup line.
At the motel, Sam checks the Internet and confirms that there have been six further lake disappearances going back 35 years, and whatever is responsible is picking up speed. One of the victims is Christopher Barr, Lucas' father. He took Lucas out swimming, drowned, and Lucas was stranded alone on a floating platform for two hours before rescuers found him. They find Andrea and Lucas in the park and Dean attempts to draw the boy out. He says that he saw something happen to his mother when he was young, and suggests that Lucas could just draw him a picture of what he saw on the lake. At first he believes he has failed, and goes back to talk to Andrea. She says that Lucas is suffering from post-traumatic stress. As the brothers prepare to go, Lucas brings Dean a picture of a house.
At the Carlton home, Will offers to make dinner. His father, depressed, doesn't respond. Will is working alone when the kitchen sink fills with dirty water. Will tries to clear the clog, but something in the dark water grabs his hand and pulls his head and shoulders into the sink. He drowns quickly and silently. After his death, the water mysteriously drains out of the sink.
Sam learns of Will's death and tells Dean what happened. Theorizing the two drownings are connected, the Winchesters speculate that they may be dealing with a water wraith or some kind of demon, and that its ability to go anywhere the lake water goes makes it very dangerous. Since the lake is being drained, whatever is responsible is acting before the lake is gone. Sam confirms that Christopher Barr was Bill Carlton's godson. They go to see Bill, who refuses to talk to them. As they leave, Dean realizes that the Carlton home is the same house that Lucas drew for him.
Dean goes to Andrea's house and asks to talk to Lucas again. She's reluctant, but Dean asks her to let him talk to Lucas if she has the slightest suspicion that something is going on. Andrea relents, and Dean talks about how he didn't talk at first when he lost his parent. Lucas gives him another drawing, depicting a yellow two-story house behind a church, with a fence, a boy, and a bicycle in front. Realizing this may also be a real house, the Winchesters start a search. As they go, Sam says that Dean never told him about what happened to him after Mary died, and Dean insists that it's no big deal.
The brothers do some legwork and find the house. They talk to the owner, an old woman, and she explains that her son, Peter Sweeney, disappeared 35 years ago. He vanished on his way home from school one day and was never found. Dean finds a photo of Peter with another boy, Bill Carlton.
On the lake, Bill is sitting by the lake and muttering that he didn't believe, but now he understands and knows what his tormentor wants.
The brothers drive to the lake, figuring that Peter Sweeney's spirit wants revenge on Bill, who killed him. They get there as Bill pulls away from the dock in a small boat. He makes it a few hundred feet from shore before the boat is violently smashed up out of the water, then slams down and sinks beneath the waves.
The Winchesters go back to the sheriff's office, where Andrea and Lucas are there with food for Sheriff Devins. He tells them to go home, and Lucas grabs Dean's arm and starts crying. As Andrea takes her son out, Sheriff Devins talks to them about their description of events, and insists that it can't happen. He informs them that he checked and confirmed that the Winchesters aren’t Fish and Wildlife agents at all. Devins says that a witness confirmed that they weren't responsible for Bill's death, and offers them two choices: he arrests them, or they get out of town. Sam says that they'll leave.
At home, Andrea is preparing to take a bath. She notices Lucas is still awake, drawing a black whirlpool, and takes him to bed.
As they drive to the interstate, Dean turns the wrong way and heads back into town. Sam insists that the job is over now that Peter Sweeney killed Bill and has his revenge, but Dean believes that Lucas is still reacting to the ghost. Much to Sam's surprise, Dean doesn't want to leave until he's sure that Lucas is okay.
Andrea draws a bath and gets in. As she relaxes, she's unaware that lake water is pouring through the faucet. She realizes that something is trying to pull her under and tries to get out, while Lucas pounds on the door. Dean and Sam arrive in time to hear Andrea’s screams. Running in, they pull Andrea out just in time.
Afterward, Sam has Andrea tell him what happened. She says she heard a voice saying "come play with me." Meanwhile, Dean goes through the family books and finds a photo album and shows it to Andrea. She points out her father, who is in Scout troop photos with Bill and Peter, and they realize that the ghost isn't done with its vengeance. Lucas goes into a trance and takes Andrea, Sam, and Dean to the woods. The brothers have Andrea take Lucas back to the house and start digging and find Peter Sweeney’s bicycle. Sheriff Devins arrives and holds them at gunpoint, and demands to know who they are. Dean and Sam figure that Devins and Bill killed Peter, drowned him in the lake, and buried the bicycle. At the house, Andrea sees her father, sends Lucas to his room, and comes out as Dean and Sam warn the sheriff that Peter's spirit will kill Andrea and Lucas, and then come for him. they ask where he buried the body, unaware that Lucas has witnessed the entire exchange and has run off.
Andrea demands the truth from her father, and he finally admits that he and Bill killed Peter. As children, Devins and Bill used to bully Sweeney. One day they were playing a “game” by holding his head underwater at the lake. But the game went too far and Peter drowned. They let the body go and it sank. Dean says that they have to get them away from the lake, but then they notice that Lucas has gone to the edge of the lake to find one of his toy soldiers floating in the water. They run to the lake, but they're too late. Peter's spirit pulls Lucas beneath the water, and then glares at Devins. Dean and Sam dive in after Lucas but are unable to find him.
Desperate, Devins wades into the water and calls out to Peter, apologizing and begging the spirit to let Lucas go and take him again. The spirit rises up beneath him, grabs his legs, and pulls him down into the depths. Dean dives back down, finds Lucas, and brings him to the surface.
Later, Sam and Dean are preparing to leave town and Sam tries to reassure Dean, saying they can't save everyone. Andrea and Lucas arrive, and Lucas calls to them by name. They've brought lunch for the road, and Dean helps him take it to the car. Sam asks Andrea how she's doing, and she says that it will take a while to absorb everything that happened. She thanks them for saving her son, and says that she'll hold onto the fact that her father sacrificed himself to save Lucas. Meanwhile, Dean tells Lucas to take care of Andrea, who gives Dean a kiss in thanks.