Sylvie Devereaux, a 25-year-old New Yorker, sneaks into Barclay Manor, a remote Scottish estate, while on a trip with her boyfriend, Aaron. She photographs an heirloom typewriter in the manor's library but is caught by the owner, who accuses her of spying for his sister, smashes her phone, and orders her out. She later identifies him as Killian Barclay, the eldest of four siblings and a recluse who has lived alone in the manor since his parents died in a car accident when he was 18.
Back in New York, Sylvie's life collapses. Her parents, Torrence and Yuri Devereaux, both famous artists, cut off her allowance months earlier. She discovers Aaron in bed with her best friend, Margot, and an eviction notice appears on her door. With no money, no support, and no friends, Sylvie is at rock bottom.
Killian's sister, Anna Barclay, arrives with a proposal. Under the Barclay family trust, if Killian remains married for one year, ownership of the manor passes to his wife. Anna offers Sylvie 10 million dollars to marry Killian, endure the year, and sign the deed over to the family's aunt, Lorna. Killian believes the marriage is simply a strategy to improve his public reputation. After Sylvie's mother dismisses the engagement as another attention-seeking lie, Sylvie accepts, determined to prove her wrong and secure financial independence.
Sylvie flies to Scotland and marries Killian in a tense ceremony. They agree to avoid each other for 12 months. Killian calls her a "selfish, rude, ugly, entitled cow," and Sylvie threatens to make his life hell if he jeopardizes her payout. That night, a drunken Killian slashes his hand on broken glass and passes out. Sylvie bandages his wound despite his cruelty. Killian's youngest brother, Lachy, privately reveals that the family suspects Killian has not left the house in nearly 10 years and that the scheme is less about the property than about freeing him from grief.
Anna pressures the couple to appear publicly together, so Killian hosts a dinner party with his university friends instead of leaving the manor. To maintain their cover, he kisses Sylvie in front of the group, and she melts into it. That evening, Killian's best friend, Liam McNeil, makes advances on Sylvie. Killian drags her upstairs, and they have their most explosive argument yet: Sylvie accuses him of pushing her toward Liam to justify his own infidelity. He pins her to the bed, and when he spots tears in her eyes, he is unsettled.
Over the following months, their antagonism shifts. Sylvie finds a book called
The Act of Submission in the library and grows curious about Killian's interest in BDSM, sexual practices involving bondage, discipline, dominance, and submission. When Sylvie becomes lost in the city after dark, Killian drives into town to find her, leaving the manor for the first time in years. His panicked fury reveals his feelings. Back at the manor, he kisses her on the stairs, and the encounter escalates. Neither speaks afterward.
Sylvie tells Killian the physical encounters cannot continue. He argues they could maintain a purely physical arrangement. She relents. On Christmas Day they exchange intimate gifts, and Killian tells her she is delusional if she thinks any of this has been pretending. She convinces him to attend Aunt Lorna's New Year's Eve party, where Lorna blames Killian for his parents' death. Sylvie confronts the older woman, warning her never to speak to Killian that way again. That night they consummate the marriage. He tells her he is making her his; she echoes his words.
Their connection deepens. Killian reads Sylvie's novel-in-progress,
Idle Hands, typed on the old typewriter, and discovers a line: "He's the last person on earth I want to love, but I can't help it. I do." He cares for her through a fever and shows her the property's beehives and horse. At his birthday party, the evening escalates when Killian demands Sylvie declare she is his in front of their friends. She resists before finally crying out that she is.
Sylvie's parents arrive at the manor unannounced. When her mother calls Sylvie "an entitled little bitch," Killian flips the tea table, drags both parents to the door, and throws them into the rain, shouting that he loves Sylvie. She runs into the woods, screaming that no one could love her if her own parents don't. Killian chases her, vowing to love her enough for all of them. That night, at Sylvie's request, he uses a paddle on her, giving her a safe word and coaching her through the pain as she releases years of grief. She tells him she loves him for the first time. He says it back.
Sylvie takes Killian on a weekend trip to the coast, but in the night he has a severe panic attack. He reveals the full story of his parents' death: He was driving to pick up Anna and collided head-on with their car. His father was drunk, and both parents died on impact. Eighteen-year-old Killian waited alone with their bodies until help arrived. Shaken, Sylvie drives to Anna and demands the contract be voided. Anna explains it is airtight: The only way for Killian to keep the house is if the marriage fails before the year ends. Sylvie resolves to tell Killian the truth and convince him to divorce before the deadline.
Before Sylvie can confess, Anna tells Killian everything. Sylvie wakes to find her suitcases packed. Killian, drunk and refusing eye contact, insists she leave so the marriage fails and he keeps the house. He adds that he is sparing her from a life trapped with his grief. She leaves her manuscript on the library table and departs without looking back.
Divorce papers arrive just before the one-year anniversary. Sylvie signs them while sobbing and rents an apartment in Manhattan. Two months later, Killian texts that he liked her novel's ending. They begin exchanging messages and calls. He is seeing a therapist and slowly venturing beyond the manor. He asks Sylvie not to put her life on hold, but she tells him she will always wait. Over the following months, Killian drives into town alone and travels to London with Anna, rebuilding his independence.
Sylvie encounters her mother unexpectedly at a gallery where she works part-time. Torrence tells her that she and Yuri were terrible parents, that there was never anything wrong with Sylvie, and that she is proud. Sylvie does not forgive her on the spot but feels the weight of parental rejection begin to lift.
Anna calls in a panic: Killian dropped off the manor's deed at Aunt Lorna's house and vanished. Sylvie rushes to pack for Scotland but spots Killian sitting on her stoop. She launches herself into his arms. He explains that after she told him she would always wait, he knew he had to come to her. He gave the house to Lorna willingly, saying Sylvie is all he needs. They remarry the next day at the City Clerk's office with no contracts, no millions, and no schemes. In an epilogue one year later, Aunt Lorna dies and leaves the manor to Killian, who declines it. Sylvie tells him she is proud, and the novel closes with the two of them together.