Danny (JONAH BOBO) is a 6-year-old kid with low self-esteem stemming from his parents' divorce as well as his older brother, Walter (JOSH HUTCHERSON), viewing him as nothing but a cheating, juvenile pest. Danny desperately wants Walter to play with him, but the 10-year-old with rather play catch with their Dad (TIM ROBBINS).
Unfortunately, he's too busy with work and briefly has to leave them under the care of their teenage sister Lisa (KRISTEN STEWART) who wants to stay in bed until her date that night and tells her brothers not to bother her unless the house is burning down. Little does she know, however, what sort of adventure they're about to embark on.
That starts when Danny discovers an old board game in their dad's new, but old house. Titled "Zathura: A Space Adventure," it's a simple game where with the push of a button, mechanical figures lurch across the board with their final stopping point ejecting a card with a message written on it. The first warns the boys to take evasive action and that's because a meteor shower suddenly rains down onto their living room, sending them flying for cover in the fireplace.
They then discover that Danny's first move with the game has sent them, their home and a small piece of ground below it somewhere deep into outer space. Realizing they must play the game through till they reach the end to try to get home, the brothers alternate turns. With that resulting in Lisa being frozen in suspended animation, a wayward astronaut (DAX SHEPARD) ending up in their company, and a race of lizard-like, meat eating aliens appearing on their doorstep, the brothers must put aside their differences and work together to survive and get back home.