It’s the summer before their freshman year of high school, and Cooper and his three friends, Gordy, Lunk and Hiro (short for Hiroko), are on vacation with their families at Lake Geneva.
While spending the afternoon on their boat, The Getaway, Gordy convinces Cooper to play a prank on a neighboring boat, the Krypto Night. Hiro doesn’t think it’s a good idea, but she acts as lookout for Cooper and Gordy when they hide rotten fish on board. As Cooper swims back to The Getaway, he’s inexplicably afraid of the water. Gordy helps Cooper make it back to the boat without drowning. Cooper refuses to talk about the incident.
While the three friends are waiting for Lunk to arrive, they see a camera flash aboard the Krypto Night, hear a female scream and a splash, followed by the boat driving erratically. Hiro thinks the girl who screamed was thrown from the boat and that the driver hit her, but it’s too dark to tell for certain. Fearing the worst, Hiro calls 9-1-1.
Before the police arrive, the Krypto Night’s captain, Tommy Kryptoski, steers his boat near The Getaway. He explains that after he and his girlfriend had a fight, she jumped overboard and swam to shore. Hiro and Cooper meet the police ashore and tell them what happened.
Lunk arrives, and as Hiro and Cooper fill him in on what happened, a girl in soaking wet clothes walks up the beach. She claims to be Lynn, Tommy’s girlfriend, and corroborates his story, saying she jumped out of the boat and swam to shore. Cooper and Lunk think the issue is settled, but Hiro senses something is wrong. Hiro watches Tommy talk to a mysterious man in a black truck before returning to his boat.
After the group goes to Scoops, the local ice cream shop, Hiro notices the same black truck from the beach. The driver enters Scoops, and Hiro has another uneasy feeling. Once they’ve finished their ice cream, Hiro returns to the hotel where their families are staying, and the boys ride their bikes back to the beach. On the way, the black truck speeds toward them, and its side view mirror hits Cooper in the shoulder. Cooper’s shoulder is bruised, but his helmet saves him from further injury.
The morning after the incident, Tommy and Lynn are searching the beach. When they’re gone, Hiro and the boys try to find whatever the couple was looking for. During the search, Lynn approaches Hiro and reveals that the camera is missing. She asks them to keep an eye out for it. In town, Hiro sees Officer Tarpy, the officer who responded to her call the night before, and tells him about the missing camera and her suspicion that Lynn wasn’t the girl on the boat. He doesn’t seem concerned.
Later at Scoops, Hiro asks the girl at the counter if she knows the man from the night before. She identifies him by his usual ice cream flavor, Fat Elvis, and says he’s a creep who works for a nearby casino, cleaning up after the boss’ son, Tommy. When Hiro discovers that a girl named Wendy is missing, she’s convinced the missing camera will prove that Wendy was the girl on the boat.
While visiting a county fair with their families, Hiro spots Fat Elvis. As Hiro watches from the ride she and the boys are on, she gets the feeling that Fat Elvis is actually Joseph Stein, a man they caught stealing money from his business partner the previous year. The boys think Hiro is paranoid. They’re convinced Stein is in hiding and couldn’t possibly be Fat Elvis. Hiro can’t shake the bad feeling and decides to call Detective Hammer, the detective who worked the Joseph Stein case. He promises to come to Lake Geneva and check things out.
The boys still don’t believe Hiro, but they decide to stand behind her. They spend the next day looking for the camera. Cooper, who has tried to fight his fear of drowning, is looking in the water for the camera and has a panic attack just as Tommy approaches in the Krypto Night. Seeing his panic, Tommy taunts Cooper by asking him to check his propeller and rudder, which aren’t working. To save face, Cooper agrees. Once Tommy is gone, Cooper reveals that the camera is stuck on the rudder, but he couldn’t get it free. The group launches a plan to retrieve the camera. Cooper faces his fear of being underwater, and with Lunk’s help, dislodges the camera. The camera gives the police proof that Tommy murdered Wendy.
That night, Hiro receives a text message from Cooper’s phone, asking her to meet him. She discovers that Fat Elvis took Cooper’s phone at the fair and used it to lure her. Hiro is right: Fat Elvis is Joseph Stein. He plans to kill her as revenge for exposing him as a criminal the year prior. Her friends realize what’s happened. They call 9-1-1 before rushing to find her.
They find her just as Detective Hammer arrives and shoots Stein in the shoulder. Later, they discover that Stein was hired by Tommy’s father as a henchman to cover up their crimes, including Wendy’s murder. Stein and Tommy are brought to justice, and Gordy, Lunk, Cooper and Hiro enjoy the rest of their vacation in peace.