Augustine Lofthouse, a driven scientist, is tirelessly searching for habitable planets where humanity could sustain life. His journey begins at a gala where he meets Jean Sullivan, leading to a romantic relationship. Unfortunately, as his obsession with work grows, Jean leaves him after a pregnancy scare, unable to connect emotionally with him. Years later, Augustine unexpectedly encounters Jean and discovers they share a daughter, but he chooses to keep his distance from them.
Fast forward to 2049, where a devastating event has ravaged Earth, decimating the population and leaving Augustine, now in the Arctic, facing his terminal illness that demands dialysis. Despite the impending doom, he refuses to evacuate his post, intent on warning any active space missions about the dire situation. Unfortunately, most missions have been decommissioned, leaving only the spacecraft Æther still operational, returning from its exploration of K-23, a moon Augustine had once discovered. However, as he attempts to reach out, he realizes that his efforts are thwarted by a weak signal.
During a night of solitude, Augustine discovers a mute young girl in the base, who he learns is named Iris. A bond begins to blossom between them, as they journey to another base in hopes of establishing contact with Æther. Faced with merciless Arctic conditions, Augustine's health declines further when he loses his dialysis equipment. Upon arriving at the new base, he manages to establish contact but is short-lived due to a meteor strike that disrupts their communication.
Aboard Æther, the crew, including the pregnant Sully and her partner Commander Adewole, are unaware of the developing crisis on Earth. They engage in a risky spacewalk to repair their vessel's systems but are met with disaster when another meteor strike claims the life of their flight engineer, Maya, despite the efforts of Sanchez to save her. In the aftermath, Sully reaches out to Augustine, who advises her to abandon Earth and instead pursue a new life on K-23.
In a twist of fate, Sully learns she is connected to Augustine through her mother, Jean, leading to an emotional revelation that she is the daughter he never knew he had. As Augustine's health deteriorates and with the threat of radiation looming, he has a heartfelt exchange with Sully, expressing his pride upon finally meeting her, despite the circumstances. Sully and Adewole emerge as the last survivors with a hopeful mission to find a future for humanity on K-23, marking the dawn of a new era in human exploration.
