Jim White, a middle-aged father on the last day of his family vacation, wakes up to a phone call informing him that he has been fired from his job. Trying to keep this distressing news from his family, he attempts to enjoy the final day of their trip to a world-famous theme park with his wife Emily, and their two young children, Sara and Elliot. The faux cheerfulness of the park surroundings contrasts sharply with his inner turmoil. As they navigate the park, Jim's attention starts to become strangely fixated on two carefree teenage French girls, following them around the park while his own family splinters with routine bickering and distractions, leading Jim further down a path of erratic behavior.

As the day progresses, Jim's grip on reality grows increasingly tenuous. The veneer of the theme park's manufactured happiness begins to slip, revealing a bizarre and disturbing underbelly. Jim starts to experience a series of increasingly surreal and alarming hallucinations that merge with the park's attractions, causing him to question his sanity. Meanwhile, unexpected and unexplainable events occur as his paranoia deepens with each bizarre encounter within the park's confines. Jim's sense of panic magnifies with the vibrant, haunting surrealism of the park seeping into his perception, making him unable to distinguish the real from the unreal in the happiest place on Earth.