An interviewer, Mary Steenburgen, engages in a profound dialogue with Thomas Harbor, portrayed by Robert Redford, the man who has scientifically verified the existence of an afterlife. This groundbreaking discovery, however, carries a heavy price, resulting in a shocking rise in suicide rates. When pressed by the interviewer about his feelings of responsibility, Thomas firmly denies any guilt. Tragically, right after this exchange, a member of the crew tragically takes his own life live on air.
Two years after this pivotal discovery, Thomas's son Will, played by Jason Segel, finds himself on a ferry where he encounters Isla, embodied by Rooney Mara. Their conversation reveals that Will recognizes Isla's face, though he doesn't quite remember from where. Expressing his grief over the ongoing suicides, Will feels despair, while Isla provocatively suggests that such an act might be an easy escape. Will shares a peculiar incident from when he was briefly declared dead, recalling a vision of a young boy on a beach.
Soon, Will's brother Toby, depicted by Jesse Plemons, picks him up, taking him to their father's isolated mansion, where Thomas has established his new operations. Here, Will unearths the unsettling truth that all the staff there are individuals who have attempted suicide. As they delve deeper into the mansion, Will meets Lacey, played by Riley Keough, and Cooper, portrayed by Ron Canada, only to discover his father bound to a machine that continuously kills and revives him. In a moment of anger, Will confronts Thomas about the surge in suicides, blaming him for the consequences of his findings.
Later, Will spots Isla once more, this time on the beach where she walks into the water with a weighted backpack. Acting quickly, he rushes to save her from drowning and brings her back to the safety of the mansion. There, she becomes part of their peculiar household. During an unsettling meeting, Thomas reveals he has invented a machine capable of recording the visions of those who have died, but it comes with a chilling requirement: they must use the corpse of a deceased individual, leading them to steal the body of Pat Phillips.
In a moment of vulnerability, Will confides in Isla about his mother's suicide during his youth. The next day, when they attempt to capture images of the afterlife, they are met with utter failure. Undeterred, Will later sneaks into the machine room, reattaching a piece of wiring he had previously removed. To his astonishment, the machine begins to reveal a sequence of Pat Phillips' journey to a hospital, including a visit marred by conflict with a woman. Driven by curiosity, Will searches for this hospital online, only to learn that significant renovations have erased the very hallway seen in the recording.
As tension mounts during another meeting, Thomas publicly confronts Lacey regarding her disclosure about the device’s failures to others in the mansion, demanding her immediate departure. In a subsequent visit to the hospital, Will shows Isla the recording, leading them both to the realization that the machine may be capturing memories rather than actual glimpses of the afterlife. In their quest for clarity, they discover a file connected to Pat Phillips, which unravels further mysteries about his past.
Afterward, Isla uncovers a crucial detail: the man in the recording sports a different tattoo than the one she had seen on Pat. On a beach outing, Isla opens up to Will, revealing the tragic loss of her son who passed while she was asleep. Their bond deepens as they embark on a quest to locate the woman seen in the video, ultimately finding Pat's sister Janice. Janice reveals a painful memory where Pat abandoned her while caring for their father, adding layers to the narrative.
As Will and Isla draw closer, they share a tender kiss, which is abruptly interrupted by Toby. In a frantic rush, they flee to find Thomas—now lifeless and hooked to the machine. Observing his experiences, they taper onto a haunting memory: the night of their mother's suicide, where Thomas intervenes. After reviving him, Thomas shares an alarming conclusion: the afterlife may simply reflect alternative choices in their existing lives. Realizing the potential impact of this discovery, they decide to destroy the machine to prevent a surge in suicides fueled by the desire to escape their realities.
In a shocking turn of events, during a speech Thomas is set to deliver, Lacey shoots Isla, claiming she has merely "relocated" her. Tragically, Isla dies in Will's arms, leaving him heartbroken. Consumed by despair, Will hooks himself into the machine in a desperate attempt to undo the past. He finds himself back on the ferry, where he once again encounters Isla, who reveals that this is all merely a memory. It becomes clear that Will is trapped in a repetitive cycle, desperately seeking to prevent Isla's death while starting anew on the ferry each time.
Isla assures Will, claiming that he saved her, and together they will finally move on. Despite Toby and Thomas's frantic attempts to revive him, Will succumbs, promising Isla that he will never forget her. In a poignant final moment, Will stands on the beach, witnessing a young boy in the water. As the boy's mother, Isla, approaches to thank him, they are strangers to one another, and upon her departure, Will walks away, slowly beginning to remember the significance of their connection before standing still to reflect.
