While playing a mysterious game called Zathura in the basement of their old house, two squabbling brothers are propelled into deepest, darkest space. On their fantastic journey, they are joined by a stranded astronaut and must survive meteor showers, hostile lizard-like aliens, a rocket-propelled robot run amok and an intergalactic spaceship battle. But their greatest peril lies ahead. For unless they finish the game and reach the planet Zathura, they are doomed to be trapped in outer space forever.