In the near future, a team blasts off on a two-year trip to Mars. Collette stars as the ship’s commander, Marina Barnett, who’s making her third and final journey to the colony there. Kendrick is the mission’s medical researcher, Zoe Levenson; Kim is biologist David Kim, who’s studying the respiratory possibilities of algae. They’ve been chosen from thousands of applicants and undergone extensive training. But the film reveals in small, subtle ways that these two are indeed regular people and not superhuman astronauts. David suffers from vertigo and vomits not long after takeoff; Zoe’s delicate charm necklace floats up toward her face to indicate a loss of gravity, and once they’ve docked she unbuckles and exclaims to Marina: “Are you kidding? That was incredible!” (“Stowaway” depicts space travel, at least initially, not as a process that’s smooth and tranquil, but rather one that shakes you to your bones, to your core.)
While they’re all upbeat and provide polished, perfunctory answers during an initial television interview from space, their polite workmanship is shattered with the realization that they’re not alone. There’s a man—hidden, unconscious and bleeding—in the ship’s hull, which Marina discovers when he comes crashing through the ceiling on top of her, breaking her left arm as she tries to catch him. When he comes to, the crew discovers that his name is Michael Adams (Anderson) and he’s a launch crew engineer and graduate student. Somehow, he got knocked out during final checks and became trapped, unbeknownst to anyone. Now, he’s unwittingly hurtling through space. How is this sort of thing possible? I’m not an aeronautical engineer—I got a C in chemistry in high school, hence I write about movies for a living—but I found the explanation for Michael’s presence on board to be extremely unbelievable. The film’s production notes detail Penna and Morrison’s thorough attention to detail in wanting to make the story scientifically accurate, and it probably is, but this crucial plot point just seemed impossible.
Regardless, he’s there, so four people are now using up the ship’s resources instead of just three, for whom they already were going to be stretched thin within this cramped area. He understandably freaks out when he realizes he’s in space—there’s a great shot of him seeing Earth from afar amid the blackness—and Anderson makes his sense of panic palpable. Additionally, he’s left his younger sister, for whom he serves as legal guardian, alone back home. But the real crisis is that Michael critically damaged the carbon dioxide-scrubbing mechanism when he crashed through the hull, making it impossible for everyone to have enough oxygen to survive the entire journey.