Maya Tanaka, a Japanese American artist and development manager at a Los Angeles museum, met her husband Noah Byatt when he wandered into one of her graduate symposium talks. Noah, a physicist at NASA's Jet Propulsion Laboratory (JPL), was drawn to Maya's openness. On their fourth date, she discovered a photograph of a baby in his nightstand: Serena, Noah's daughter from his first marriage to Eileen Merrick, a biologist. Serena died at three years and nine months from undiagnosed pediatric cardiomyopathy, a rare heart condition. The marriage dissolved, and Eileen moved away. Noah's grief remained a layer beneath everything.
Before meeting Maya, Noah published a controversial paper arguing that human consciousness arises from quantum mechanics and can participate in entanglement, a phenomenon in which particles share information across distance. His peers mocked the paper, and the humiliation drove him from theoretical into experimental work at JPL.
One evening, Noah comes home with urgent news. Klein Michaels, a reclusive billionaire, has quoted Noah's discredited paper from memory and revealed a secret project: His team has built a machine that enables a person's present consciousness to entangle with a past version of itself, allowing the subject to travel into their own memories. Klein offers Noah a position at his compound in Marfa, Texas, and Noah agrees.
Maya sees the move as a new beginning. She can reconnect with painting, and perhaps Marfa will be the right time to try for a baby, something she wants but Noah has avoided committing to. On the drive, she raises the topic. Noah says "I agree," which both recognize as a non-answer.
At the compound, the house eerily replicates Noah and Eileen's old Los Feliz home, including a navy suede couch identical to one Serena once drooled on. Noah notices but says nothing. Inside a windowless structure called Building D, Klein and lab director Nils Olsson show Noah two black, coffin-shaped sensory-deprivation baths. Through a process Klein calls Episodic Folding, nanorepeaters and a psychoactive Fold Cocktail enable a subject's present consciousness to entangle with a past memory while the bath's electromagnetic core sustains the connection. Noah undergoes a brief session and vividly hears Serena's voice. Then Klein reveals Noah was hired not to build models but to be the human test subject.
Maya visits the Chinati Foundation's Donald Judd sculptures and witnesses a pronghorn, a graceful animal native to the region, charge a concrete wall and die. She begins painting the pronghorn in vibrant abstract canvases. Justine Koppelman, a gallery owner Klein connected her with, loves the work but rejects references to the animals' deaths, wanting to use Maya as a bridge to Klein's money. Frustrated, Maya reconnects with Ren Hayashi, her ex-boyfriend from Portland. Now in Tokyo, Ren encourages her to trust her creative instincts.
Noah, consumed by training, secretly maps memories of Serena. When Maya learns from Nils that Noah has been speaking to Eileen about the project, she confronts him. At the Marfa Lights viewing area, Noah confesses he called Eileen because she knew Serena in a way Maya never will. Maya announces she is leaving for Tokyo. "We're already broken," she says.
Klein privately reveals his true ambition: not merely observing memories but effecting causal change. He was a major investor in a failed space mission and wants to fold back to erase that humiliation. Noah realizes Klein has been exploiting his grief all along.
Noah's first fold, a locked-box test designed to prove time travel, fails. That night, he folds alone to Serena's bedroom and watches her sleep. When Maya pounds on Building D's door, she tells him she has bought a plane ticket. He shares the story of realizing he loved her: an ordinary evening when he was cooking and she was reading, and he felt the impulse to stay alive for her. They part.
Noah texts Eileen: "Come to Marfa. I saw her." Eileen has been rebuilding a quiet life in Northern California, dating Prem, a kind chemistry professor. She drives to the compound. Together, she and Noah discover hidden cameras in the house and a photograph of Talia Bolson and her husband, Curtis. Noah recognizes Talia's name from a business card in Nils's office. They drive to El Paso and find Talia visibly ill. Curtis explains that each fold delivers dangerous radiation, the nanorepeaters damage kidneys, and the effects worsen with use. Klein exploited Talia's guilt over an accident that killed her niece, compelling her to fold without informed consent.
In Tokyo, Maya reunites with Ren and reconnects with her parents. Her father asks what she has given up, telling her that nothing distorts time the way having a child does. At a party, Maya discovers a camera obscura effect: Light streaming through a small opening projects an inverted image on the opposite wall. She is moved by how a shift in perspective transforms something familiar.
Back in Marfa, Eileen folds to Serena's last bedtime and discovers that the bedroom door she always believed Noah closed the night Serena died was, in the fold, open. She and Noah then fold together to that night. Noah deviates from what happened, trying to drive Serena to the hospital. Eileen, holding Serena and feeling her small hot breath, tells him to stop. Afterward, Eileen tells Noah he has been searching for a way to reverse the irreversible when what matters is the permanence: Serena's death cannot be changed, but her life will always be theirs. They fold once more, to Serena's birth, and simply remain without trying to alter anything.
Eileen examines the bath's construction and realizes its hydrogen fuel cell and the core's reactive gases can destroy the machine. She calls Maya, who was already planning to return.
Maya arrives in Marfa, and the three plan the destruction. Maya arranges for a journalist named Belinda to serve as witness. Noah takes Maya on a final fold to meet Serena. Maya hides in a closet and watches as Noah and three-year-old Serena place glow-in-the-dark stars on the ceiling. Noah coins the word "lightbreaker": something that breaks light but transforms it into something unimaginably new. That night, he tells Maya he wants to try for a baby.
On the morning of his last fold, Noah completes the locked-box test, reading a passage from T.S. Eliot's
Four Quartets. He reflects that Klein's promise of a redeemable past was a lie: Possibility exists not in unlocking the past but in what springs forward each new second. He willingly exits the fold, drains the bath, introduces hydrogen into the core, and runs. The explosion cracks through the compound.
Belinda files her story, including an anonymous tip about the pronghorn deaths and Klein's responsibility. Noah smuggles design schematics and a list of former employees to bring to JPL so the technology cannot remain under Klein's sole control.
The three stand with packed suitcases. Eileen tells Noah to follow Maya's lead. Maya tells Eileen she is family. Eighteen months later, Maya gives birth to a boy named Sol. Eileen, now living with Prem in Vancouver, comes to meet him. Maya whispers, "Serena's half brother." Maya and Noah drive out of Marfa. Eileen visits the Robert Irwin Light and Space installation alone, walking from darkness into overwhelming brightness and thinking, "This art is about living." All three move forward toward light that has not happened yet.