After their father leaves for work, leaving them in the care of their older sister, six-year-old Danny and ten-year old Walter discover an old tattered metal board game, "Zathura." After trying unsuccessfully to get his brother to play the game with him, Danny starts to play on his own. From his first move, Danny realizes this is no ordinary board game. His spaceship marker moves by itself and when it lands on a space, a card is ejected, which reads: "Meteor shower, take evasive action." The house is immediately pummeled from above by hot, molten meteors. When Danny and Walter look up through the gaping hole in their roof, they discover, to their horror that they have propelled into deepest, darkest outer space. And they are not alone. Danny and Walter realize that unless they finish the game they'll be trapped in outer space forever. With every turn, they confront one incredible obstacle after another: They accidentally put their sister Lisa into a deep cryonic sleep, are chased by a crazed, malfunctioning six-foot robot, rescue a stranded astronaut and are besieged by lizard-like, carnivorous creatures called Zorgons. With the help of the astronaut, Danny and Walter begin to put their petty fraternal differences aside, work together to overcome the obstacles they encounter and attempt to finish the game so they can go home. But all their efforts may be in vain when they face their biggest challenge of all--a battle against an intense gravitational pull into the void of the dark planet Zathura.

Two squabbling brothers are propelled into deepest, darkest space while playing a mysterious game they discovered in the basement of their old house.