A young boy named Peter is dismayed to learn that his beloved bedroom will be given to his grandfather, Ed, who has recently moved in with their family. Peter is upset about being relocated to the attic and contemplates the unfairness of the situation. He discusses his predicament with friends at school, and they suggest he take matters into his own hands by declaring a "war" on his grandfather to reclaim his room. Being somewhat mischievous and resourceful, Peter decides to go for it and begins to execute a series of pranks designed to annoy Ed and persuade him to move out of the room.

The pranks escalate, with Ed discovering that Peter is behind the antics. Rather than taking it lightly, Ed decides to engage in the battle, launching his own counterattacks in this intergenerational war. Both sides see the exchange as harmless fun initially, yet tensions start to rise as each new stunt becomes increasingly elaborate. This playful rivalry causes unexpected chaos within the household and exposes deeper family dynamics as both Peter and Ed begin questioning the rationale behind their feud. As the situation intensifies, they are forced to confront their feelings, but everything comes full circle with both a resolution to their conflict and a reckoning for their actions. However, the heart of the story lies not just in their pranks but in the valuable lessons they both learn about understanding, acceptance, and family bonds.