Without a job, a young man is given the opportunity to run his ill uncle's private-detective agency. He finds himself mixed up with everything from an unfaithful husband who is a secret nudist to a schoolteacher who believes his pupil's father is beating him.

William has to spend another boring Sunday with his grandparents. He has only a box of Lego and his imagination for comfort. Gradually the crises aboard his spaceship become entangled with the fate of his sleeping grandmother.