The movie follows the adventures of Greg Heffley, a middle school student, as he gears up for his summer break. At first, Greg is excited about the endless possibilities that come with having no school, but soon he realizes that his plans have gone awry and he has nothing to do.
Desperate to escape the summer doldrums, Greg tags along with his best friend Rowley to the exclusive country club where Rowley’s family is a member. But when the two get caught pretending to be members, their antics result in a loss of privileges. Greg is left to fend for himself at home while Rowley and his family go off on vacation.
Throughout the summer, Greg’s relationship with his parents and older brother becomes increasingly strained. As he tries to fill up his days with odd jobs, outdoor activities, and playing video games, he begins to realize that his summer might not be as glamorous as he had hoped.
When Greg stumbles upon a cute employee at the local water park, he decides to pursue her and even lies about his identity to get closer to her. But things quickly spiral out of control and Greg ends up getting into trouble.
In the end, Greg learns the value of honesty and hard work, and realizes that sometimes the best adventures are the ones found close to home.