Dr. Emery Martín is a brilliant scientist living a double life. To the outside world, including her husband, she manages surgical laser projects at SurgOptix. In reality, she works in BioNEX, a secret underground laboratory hidden beneath the SurgOptix building, where she has developed the BioVIVE, a medical pod capable of diagnosing and healing disease. Her most ambitious and unauthorized project is Compound Y, a substance that can keep a dead person's heart beating and brain functioning long enough to place them in the BioVIVE for revival.
Three years earlier, Emery met Luca Martín, a charming Italian American landscaper, at a cousin's wedding in Las Vegas. Despite being opposites, their chemistry was instant. They married in San Diego weeks later, with Emery knowing she could never tell Luca the truth about her job.
By their third anniversary, the marriage is strained. Emery works obsessive hours and forgets their anniversary entirely. Luca, a warm man conditioned by a neglectful childhood to accept absent partners, channels his frustration into running and home projects. On the anniversary morning, Emery rushes to BioNEX for the biggest presentation of her career. Her demonstration of the BioVIVE's success in treating terminally ill animals impresses an international board, but Dr. Vincent "Vince" Barker, a jealous rival scientist, publicly reveals her unauthorized resurrection research. The board pauses her project. Worried that Vince might tamper with the compound, Emery and her best friend, Dr. Annabella "Annie" Rodriguez, a veterinarian and collaborator on the BioVIVE trials, move the remaining vials of Compound Y out of the lab.
Racing home hours late, Emery calls Luca, who is out on a run. He tells her to wait at the bottom of their street and adds that they need to talk. As she watches from her parked car, a speeding vehicle strikes Luca in the crosswalk. Emery discovers that his femoral artery has been nicked, finds no pulse, and begins CPR. Remembering the cooler of Compound Y in her back seat, she injects the compound directly into his heart rather than wait for an ambulance she knows cannot arrive in time.
Emery calls Annie, and together they smuggle Luca into BioNEX on a gurney, bluffing past security by claiming they are transporting an injured Great Dane. They place Luca in the BioVIVE pod and initiate the revival sequence. His vitals stabilize, and he takes his first conscious breath.
When Luca opens his eyes, he has no memory of his life. He retains language and procedural knowledge, but every personal experience is gone. He does not recognize Emery or know his own name. After initial suspicion that she may have harmed him to test the technology, he accepts her explanation and allows her to bring him home.
The following days are consumed by crisis management. Annie arranges for a discreet cleaner to erase evidence from the street and Emery's car and delivers medical equipment to the house. She also brings Honey, a golden retriever-husky mix and the first animal successfully revived by the BioVIVE, to stay with Luca as a companion. Emery sneaks back into BioNEX to delete security footage of their unauthorized nighttime entry, though she discovers a thirty-day backup exists. Their elderly neighbor, Betty Caldwell, a vigilant widow, confronts Emery: Betty watched from her window and saw what appeared to be Emery stabbing Luca and loading his body into her car. Because Compound Y requires a forceful injection through tissue and bone to reach the heart, the act looked exactly like a stabbing from a distance.
With the secret forced into the open, Emery confesses everything to Luca: her real career, the hidden safe in her office, and her recognition that she exploited his willingness to accept an absent partner. When Luca asks what she wants from the marriage, Emery tells him she wants him to recover his memory and for them to start over with full honesty. She promises to quit her job if necessary.
They agree to a deliberate "do-over." Emery takes Luca to the beach where they had their first date and tells him the full story of her parents' death in a car accident, revealing that the loss drove her to develop technology she believes could have saved them. They share their first post-accident kiss. Luca's best friend and business partner, Crispin "Crash" Barnett, learns the truth and helps normalize Luca's reentry into his own life.
Luca's memories begin returning in fragments: He remembers that Emery needs multiple cups of coffee to function and recalls a childhood story about Crash. Their physical relationship resumes with increasing passion. They travel to Yosemite, a place Luca loved, hoping the familiar setting will trigger more memories. There, they make love for the first time since the accident, and Luca tells Emery he loves her.
When they return home, twin crises converge. Luca discovers an engagement letter from a divorce attorney in his desk, dated one week before the anniversary, revealing he had been preparing to leave Emery. He is devastated but resolves that he loves the present-day Emery and wants to move forward. Before he can process this, he receives a threatening phone call from an unknown man who knows about the resurrection and demands Luca come to a specific address alone. Luca drives there.
Meanwhile, Emery is summoned to BioNEX, where the board of directors confronts her. Security has found Luca's phone in the lab and recovered backup footage showing two people entering the facility and three leaving. Emery confesses, and the board demands she bring Luca in for examination, revealing that the US military is interested in the project.
Racing home, Emery finds Luca gone. With Annie, Crash, and Betty, she reviews Betty's home surveillance footage and spots a figure returning Honey to their yard on a day the dog went missing. When they zoom in, Emery recognizes Vince by his distinctive ponytail. She texts Vince, who confirms he has Luca and demands she bring the compound and Honey.
At an industrial warehouse, Emery discovers that the true mastermind is not Vince but Claire Morgan, her own trusted assistant. Claire reveals she deliberately hit Luca with a car, gambling that Emery's trauma over her parents' death would drive her to use the compound rather than call for help, proving the technology works and increasing its value to international buyers. Vince was recruited as a reluctant accomplice motivated by professional jealousy. Luca's full memories return when he recognizes Claire as the driver who hit him. Claire orders Vince to kill Emery and Luca, but Vince turns the gun on Claire instead. In the ensuing struggle, Betty shoots Claire in the leg, and a second shot hits Emery in the abdomen. As Emery collapses, she tells Luca she does not blame him for wanting to leave. He tells her he never wanted to leave. Annie rushes in and injects Compound Y into Emery's chest, buying time for emergency surgery.
Emery wakes in the hospital with her memory intact. She briefly pretends not to recognize Luca, mirroring his experience, before laughing and pulling him close.
Two years later, Emery and Luca are in Bali, expecting their first daughter. Claire is serving a lengthy federal prison sentence; Vince is also imprisoned. Emery left BioNEX after a six-month consultancy to transfer the BioVIVE project to an international scientific consortium. She and Luca have been in couples therapy, working through his feelings of abandonment and her guilt. Betty has become a surrogate grandmother. Luca tells Emery that every day now feels like their treasured Sunny Sunday tradition, extended from a single weekly ritual to encompass their entire shared life.