At a middle school in a small Oregon town, 14-year-old George Tooney sets up a camera on his school basketball court to record his free-throws. While he is shooting, shy student Sam Merrick picks up the camera to take a look. Defensive and angry, George beats Sam up. Sam confides in both his protective older brother Rocky and his budding girlfriend, Millie, who urges Sam to take a higher road.
Sam's older brother Rocky confides in his friends, Clyde and Marty, who are also familiar with George's reputation as a bully (he previously mocked Clyde for having two gay dads). While they agree that they need to stand up for Sam, they have different approaches. Clyde, who is sensitive and a bit of an outsider himself within the group, is more sympathetic and passive. Marty, who has issues with anger and trauma stemming from his father's suicide, his mother's apathy and his older brother's abuse, favors a more righteous form of revenge.
Eventually, they hatch a plan with Sam to invite George on a fake birthday party for Sam, which George all-too eagerly accepts. They plan to drive to a local creek where they will spend the afternoon on a boat and, in an orchestrated game of Truth or Dare, get George to strip his clothes and jump in the lake, leading him to hitch a ride home in the nude.
When the gang consisting of Sam, Rocky, Marty, Clyde and Millie (who is not yet aware of the plan) arrive at George's house, he is working on his video diary for the day. He leaves without telling his mother where he will be, and gives Sam a present a large, high-end water gun. They run into Marty's obnoxious older brother at a convenience store on the way.
Throughout the drive and the journey to the boat it becomes clear that George, while annoying and occasionally harsh, is truly desperate to fit in and resorts to aggression as a cover-up. He also admits to having a learning disability, which he hopes to be accepted for. En route to the boat, Sam tells Millie about the plan. Millie is sympathetic to George, and asks Sam to call off the plan or she won't get on the boat.
Once they set sail, George tries to warm up the gang even more, though his attempts still come off as awkward. On a pit stop, Sam urges Rocky and Clyde to call off the plan, and both are receptive. When they relay the request to Marty, however, he lashes out, and only agrees begrudgingly. Later, on the boat, the game of truth or dare starts, and as George starts to have more fun, he becomes more aggressive and slowly wears down Marty. After making an innocent remark about fathers, which he immediately tries to retract, Marty begins to tear into George verbally, and reveals the gang's plan. Feeling betrayed and realizing it isn't even Sam's birthday, George goes on a verbal tirade against each one of the group, particularly Clyde and Marty. As he begins to repeatedly taunt Marty about his father's suicide, a fight erupts. Rocky, intervening, pushes George, causing him to fall off the boat.
No one dives in to save George right away, with none of them realizing that he can't swim. George struggles for some time until he is knocked on the head (possibly by his camera) and goes under. The others dive in and pull George from the lake, and Millie tries to revive him with CPR, but the effort is in vain and George is already dead.
Traumatized and unsure of what to do, Marty reasons that the only thing to do is bury the body. While Rocky and Millie suggest going to the police and explaining that it's an accident, Marty balks at the idea, reminding them that the video camera (which has been left in the creek) contains Marty's taped confession of the original plan. Reluctantly, they bury George and hitch a ride back to the spot where Marty's car has been left. Marty talks to his brother to tie up the loose end, and his brother agrees to not turn him in.
The others, racked with guilt, meet at Sam and Rocky's house, and decide they must go to the police. When Marty joins the group, he feels angry that they have made the decision without him, and refuses to be part of the confession. He flees with his brother's gun and his own car, holding up a gas station along the way.
The rest of the gang goes to George's house to inform her of the news. The scene then cuts to a police station, where officers question Sam about the confrontation. Several officers recover George's camera and review the footage, which includes George's video diary taped prior to the day. In it he talks about his goals for fame and popularity, his desire to be understood and the way he sees the world. George's body is exhumed as his mother, Sam and police watch.