In the opening voice-over, we hear Qualles's Sam Walden, the daughter of famous scientist Dr. Henry Walden (Danny Huston), explaining that Earth was doomed to destruction because of "human nature," establishing a stern and dreary tone that remains constant throughout the film. Given the state of the Earth in the movie's bleak future, that's not entirely surprising: A significant chunk of humanity has been wiped off the face of the planet by changes in the atmosphere, sending most survivors scurrying into space to discover a new home. Temporarily, they've taken up residence at a space station circling Io, a moon of Jupiter named for a figure from Greek mythology, but they hope to explore the galaxy further and rebuild society. Maybe find an Earth 2.
Determined and stubborn, Sam is one of the last holdouts on Earth. While maintaining a very-long-distance relationship via email with her boyfriend Elon -- no, probably not that Elon -- on Io, Sam spends most of her time conducting experiments, raising bees, and listening to her father's lectures on tape. It's a lonely, isolated existence but, like the Restoration Hardware catalog vibe of A Quiet Place, there's a quasi-aspirational quality to Sam's sealed-off method of survival. She's not happy. (Certain details about her family life are kept cryptic for plot reasons, but there are no "twists" a seasoned reader of dystopian stories shouldn't see coming.) She's not completely miserable, either.
The arrival of Mackie's Micah, a straggler left behind on Earth who travels around in a hot air balloon, changes Sam's situation. There's a shuttle leaving the planet in four days, the last one before Earth gets abandoned for good, and Micah soon insists that Sam join him. Out of loyalty to her scientist father's teachings, Sam isn't as excited to voyage into the unknown; she wants to remain behind and revive life on Earth. In between equipment repairs and expository reveals, the two share dialogue that strains for profundity: Micah quotes Plato at length and Sam explains the equation tattoo on her arm. At times, the movie resembles a ponderous but well-meaning play, like Beckett rewritten by a bot fond of platitudes like "people can change" and "people aren't meant to be alone."