Once underway, the upper stage of their launch vehicle is connected by 450-meter tethers to the ship's main hull, acting as a counterweight for inertia-based artificial gravity.

[3] Shortly after takeoff, Barnett discovers launch support engineer Michael Adams, an accidental stowaway, unconscious between two modules, entangled with a device that scrubs carbon dioxide from the air on the ship.

Barnett asks mission control for a solution that will save all four passengers, but the only option—an untested EVA (spacewalk) to climb the tethers and recover liquid oxygen from the spent upper stage rocket—is deemed too risky.

Barnett and David begin to come to terms with sacrificing Michael, but Zoe convinces them to wait ten days for mission control to think of another solution.

After regrouping, they realize that the large tank continues to leak oxygen due to the improvised connection, and that if one person exposes themselves to the lethal radiation to retrieve the cylinder left behind on the first attempt, the other three can survive.

[11] In November 2018, Sony Pictures Worldwide Acquisitions acquired the film's international distribution rights, excluding the United States.

The site's critics consensus reads, "Pacing problems prevent Stowaway from fully engaging, but it's distinguished by its thoughtful, well-acted approach to a story built on an excruciating moral dilemma.