Two brothers, Walter and Danny, discover an old mechanical board game in the basement of their house. When they start playing, they soon realize each turn in the game triggers a dangerous event in their home, transforming it into a spaceship hurtling through space. With their sister Lisa accidentally frozen in cryogenic sleep, the boys are forced to navigate a series of increasingly perilous cosmic challenges. Each card drawn brings new threats, ranging from meteor showers to hostile alien creatures, all with the goal of completing the game to return home.

As the game progresses, the brothers encounter an astronaut who becomes an essential ally, guiding them through the dangers and offering crucial survival tips. Their relationship is tested as they face morally complex decisions and dire situations that require them to trust and depend on each other. The challenges intensify, compelling Walter and Danny to work together against substantial odds, maturing in the face of adversity. Their singular hope lies in enduring the game's trials long enough to finish it and restore their normal lives on Earth.