Lake Manitoc, Wisconsin.
A teenage girl (Sophie Carlton) heads out for a swim in the lake. She thinks she hears whispering and then is grabbed from below and disappears beneath the surface.
Dean is busy trying to hit on the waitress at a diner. Sam shuts him down. Dean defends himself, telling Sam they ARE allowed to have fun once in awhile. Dean goes back to doing research and finds some suspicious deaths in Lake Manitoc, WI.
Sam is frustrated that they aren't looking for their dad. Dean assures him they will, but they're going to kill every evil thing they can find between now and then. They head to Wisconsin.
Sam and Dean pose as agents with the U.S. Wildlife Service when they show up at the door of the missing girls' home. Her brother tells them she was a varsity swimmer. They ask if he saw anything strange, but the brother says she was too far out for him to see what happened. Their father is sitting alone on the dock staring out at the lake.
Sam & Dean go to question the local sheriff, Jake. He says there is no indigenous species large enough to kill a human in that lake. Dean points out it's the 3rd missing body this year. The sheriff is frustrated that this is happening in their town. He tells them that the dam is falling apart and the lake is starting to empty and eventually there won't be a lake anymore.
The sheriff's daughter, Andrea, walks in. Of course, Dean is intrigued. She is followed by her son, Lucas, who seems shy and won't speak to Dean. Dean asks the sheriff's daughter to escort them to the nearest motel. She tells Dean is must be hard, with his sense of direction (as a U.S. Fish and Wildlife agent), the way he can't find his way to a decent pickup line.
At the hotel, Sam gets online and finds out that there have been many drowning victims in the lake over the years, including Andrea's husband (and Lucas' father) Chris who was out swimming and disappeared, leaving Lucas alone on a floating dock for hours.
Sam & Dean find Andrea and Lucas in a park. Andrea tells Sam to get Dean to stop hitting on her. Sam tells her that's not what this visit is about. Dean tries to go talk to Lucas who is drawing. Lucas doesn't respond, but Dean sits down to draw with him. Dean tells Lucas he saw something bad when he was Lucas' age. He says he'll believe him if he wants to talk. He tells Lucas he could draw him a picture of that day on the lake with his dad if he doesn't want to talk. Lucas still doesn't respond, but picks up Deans' stick figure drawing of the Winchester family after Dean leaves.
Andrea says Lucas hasn't spoken since his dad died...a form of PTSD, the doctor's say. He said Lucas' whole personality changed after the day of his father's death. Lucas walks over and hands Dean a picture he drew of a house. Andrea looks surprised.
Back at the lake house, the father of the missing girl (Bill Carlton) is inconsolable. His son (Will Carlton) says he's going to fix some dinner. As he's washing vegetables, the water starts to run brown, then begins to bubble up from the sink drain, roiling violently. It seems the drain is plugged, so the son reaches in to pull the plug and even when he does, the water doesn't drain. He reaches in again and is pulled down and held underwater by some unseen force. As soon as he is dead, the water begins to drain from the sink.
Sam tells Dean he went past the house and now Will Carlton is also dead. It seems that the victims are related and that Lucas is Bill Carlton's godson. Mr. Carlton is inconsolable with both his children gone. Sam & Dean try to question him, but he asks them to leave. Dean thinks there's something Mr. Carlton isn't telling them.
Walking back to the car, Dean realizes that the drawing Lucas gave him is a drawing of the Carlton's house.
Sam & Dean ask Andrea if they can question Lucas again. She's reluctant, but agrees. Lucas is on the floor drawing pictures of bicycles. Dean thanks him for the drawing of the house, but says he needs his help again. He asks Lucas how he knew to draw that house. Did he know something bad was going to happen? Dean tells Lucas he knows he's scared and it's okay. Dean tells Lucas how, when he was his age, he saw something horrible happen to his mom. Sam looks on sympathetically. Dean says he knows his mom would want him to be brave, and maybe Lucas' father would want him to be brave too. Lucas looks up and hands him another drawing of a building next to a church.
They head off to find the yellow two-story house that Lucas drew. Sam tries to have a meaningful talk with Dean about what happened to their mom, after what he heard Dean say to Lucas, but Dean blows him off.
At the yellow house, they find an old woman and ask if there is a little boy there who owns a red bike. She says Peter has been gone for 35 years now; he just disappeared and the police never knew what happened. She tells them that losing Peter was worse than dying; the exact same words Mr. Carlton used about the deaths of his children. Dean sees a photo of Peter and his bike with a friend...Billy Carlton; as children in 1970.
Mr. Carlton is sitting on the dock talking to the lake, saying "you've taken everything"...he says, "I think I finally know what you want."
Sam & Dean are back in the car trying to figure it out. They think maybe Bill killed Peter, and perhaps Peter's spirit wants revenge. They head to the Carlton house just in time to see Mr. Carlton heading out to the lake in a fishing boat. The boat seems to hit something and is tossed into the air. Bill Carlton disappears into the water.
Sam & Dean are back in the sheriff's office. The sheriff seems to have no leads. He tells his daughter and Lucas to go home. Lucas starts freaking out until Andrea takes him home. Dean and Sam tell the sheriff what they saw at the lake. The sheriff doesn't believe them and tells them he knows they aren't from the Wildlife Service. The sheriff threatens to arrest them for impersonating government officials or they can leave town and never look back. They agree to leave.
Andrea discovers Lucas feverishly drawing on the floor. He's drawing what looks like a black swirling vortex.
Sam & Dean are leaving town. Dean makes a U-turn and turns the car around. There's something he can't let go.
Andrea fills the bathtub.
Sam is trying to talk Dean out of going back. If the spirit wanted Bill Carlton and got him, shouldn't it be over? Dean says Lucas is still scared and he can't leave until he knows the kid is okay. Sam can't believe Dean cares so much about a child asking, "who are you and what have you done with my brother"? Dean tells him to shut up.
Andrea gets into the tub and closes her eyes. The water starts to run brown but she doesn't see. She opens her eyes to see dark brown water surrounding her. She starts to scream as something grabs her. Lucas is pounding with all of his strength on the bathroom door.
Sam & Dean are outside Andrea's house when Lucas flings open the door in a panic and leads them upstairs at a run. Dean holds Lucas back while Sam tries to pull Andrea out of the tub, but an incredibly strong force is holding her underwater. Finally she breaks free and she and Sam fall to the bathroom floor.
The next day, Andrea is afraid she's going crazy. Sam asks her to tell him everything that happened. Andrea says she thought she heard a voice saying, "come play with me".
Dean is looking through family photo albums while Sam questions Andrea. He finds an album with a photo of a scout troop. They realize that both Andrea's father Jake the sheriff and Bill Carlton were in the troop with Peter.
Lucas leads them out to the yard and looks down at the ground. Dean and Sam start digging. They hit something metal not far below the surface. It's Peter's bike. They turn around to find the sheriff pointing a gun at them wanting to know how they knew the bike was there. Dean tells the sheriff nothing stays buried.
Dean says Peter's spirit is going to take everything the sheriff loves so he can feel the pain Peter's mom felt when Bill and Sheriff Jake killed Peter. Dean says they need to find Peter's remains and salt and burn them.
Meanwhile, Lucas, alone in the house, sneaks out.
Andrea begs her dad to tell her he didn't kill anyone. He confesses that he & Billy were out on the lake when they were children and they were bullying Peter. They got rough with him holding his head underwater. They held him under too long and he drowned. They let Peter's body go and it sank. There's no corpse to salt and burn.
Jake says that Dean's theory about the spirit is irrational. But Dean says they have to get everyone away from the lake as soon as possible. They notice that Lucas is out on the dock reaching for the water. A small, cold, blue-gray hand reaches up and pulls Lucas in. The sheriff can't believe it when he sees a gray-colored Peter staring at him, eyes and forehead just above the surface before he slowly sinks under.
Sam & Dean jump in to rescue Lucas. The sheriff jumps in telling Peter to take him instead. A pale Peter rises up from below and drags him down. We see the sheriff as he disappears into the blackness.
Sam surfaces without Lucas. Andrea is frantic. Then Dean breaks the surface; Lucas is in his arms.
The next day, Dean seems down. Sam tells him they can't save everyone. Andrea and Lucas come to say goodbye; Lucas made them sandwiches for the trip. Sam asks Andrea how she's doing. She said it will just take her awhile to sort it all out, but they saved Lucas and she can't ask for more than that. She'll try to remember how much her dad loved Lucas, no matter what else he did.
Lucas is now talking. Dean asks him to repeat a "very important phrase" back to him, to which Lucas says "Zepp rules" and they high-5. Andrea kisses Dean and thanks him. (This is getting to be a habit.) Sam smiles. Dean tells him to hurry up.
They get into the Impala and drive off, music blaring.