Czech astronaut Jakub Prochazka (portrayed by Adam Sandler) is in the midst of a six-month solo mission in space, tasked with investigating a peculiar cloud of dust and particles known as Chopra, located beyond Jupiter. This enigmatic cloud emerged four years ago, and Jakub's objective is to collect its samples and return to Earth. Leading the charge, the Czech mission reaches the site just before South Korean astronauts, the first team to explore Chopra.
As Jakub navigates the vastness of space, he grapples with profound loneliness, deeply missing his wife Lenka (played by Carey Mulligan), who has ceased communication since he left her and their unborn daughter behind. Despite his harsh isolation, he learns through a message that Lenka wishes to leave him, yet Commissioner Tuma (portrayed by Isabella Rossellini), his commanding officer, intervenes to shield Jakub from the news in hopes of maintaining his fragile mental state.
Amid sleepless nights aboard the spacecraft and the relentless pressure of mission goals—compounded by a malfunctioning ship—Jakub confides in his friend Peter (depicted by Kunal Nayyar), expressing his struggles with the ship's noise, particularly the incessant toilet sounds. However, Peter, prioritizing repairs on more vital ship components, downplays the issue, leaving Jakub feeling increasingly isolated.
As days pass without any sign of Lenka, Jakub encounters a remarkable spider-like being with telepathic abilities, which he names Hanus (played by Paul Dano). This curious creature had been studying Earth and seeks to understand human mortality and loneliness. Hanus reassures Jakub that he means no harm, offering companionship in the void of space. The two form an inexplicable bond as Hanus begins to delve into Jakub's memories, uncovering intimate details about his life, including poignant moments with Lenka and the tragedies he has faced.
Exploring Jakub's past, Hanus learns of Jakub's familial struggles, including losing his father, who was an informant for the Communist Party of Czechoslovakia and was killed when Jakub was young. Overwhelmed by dreams of becoming a cosmonaut, Jakub often neglected Lenka, even leaving her when she suffered a miscarriage.
As their connection deepens, Hanus begins to feel disillusioned with humanity, especially after witnessing Jakub's emotional distance following the miscarriage. The tension escalates when a grain from the Chopra cloud infiltrates their spaceship, causing communication blackouts. Meanwhile, Hanus presents Jakub with an implanted memory of his miscarriage, intensifying Jakub's guilt for not returning to Lenka.
In a desperate bid for forgiveness, Jakub collaborates with Peter to send a message to Lenka, acknowledging his shortcomings. However, Hanus reveals that he is doomed to perish from a parasitic infection threatening his race. As their journey leads them to the remarkable Chopra cloud—an awe-inspiring remnant of the universe's birth with timelines overlapping—Hanus chooses to embrace his fate in the void of space.
Ultimately, Jakub rejects the notion of solitude, chasing after Hanus as he passes away from the infection. The mission culminates with Jakub being rescued by a South Korean spacecraft, where he and Lenka finally communicate, confronting their turbulent relationship, filled with regrets but also the promise of reconciliation.
