The story opens in a bar bathroom in Ruby Creek, British Columbia, where nineteen-year-old Nadia Dalca makes out with Tommy Koss, a casual acquaintance, and finds the experience disappointing. A dark-eyed, bearded stranger enters, uses the urinal without acknowledging them, and orders Tommy to move from the sink. After Tommy leaves, Nadia stays and chats, confiding that she has been accepted into a veterinary technician program. On impulse, she asks for a congratulatory kiss. The stranger obliges, and the kiss is electric. When she asks for another, he refuses. "Once is an accident. Twice is a mistake" (10), he tells her, calling her "Wildflower" before walking out.
Days later, the man appears at the veterinary clinic where Nadia works under Dr. Mira Thorne. It is not until Nadia encounters him at her older brother Stefan Dalca's house that she realizes the stranger is Griffin Sinclaire, Stefan's closest friend, who sold Stefan a farm called Cascade Acres. Griffin, in his mid-thirties, flees the encounter. Nadia is mortified but resolves to move on.
Two years pass. Nadia, now twenty-one, has completed her diploma and returned to work at the clinic on Gold Rush Ranch, a racehorse training facility. She keeps a journal with a "Life To-Do List" that includes building her savings, learning to ride, getting a horse, taking a tropical vacation, making love, and attending vet school. She confides to Mira, who has married Stefan and had a son named Silas, that she wants to apply but fears she is not smart enough.
Griffin arrives at Gold Rush Ranch, hired by Billie, a famed racehorse trainer, to break young horses for the summer. Ashamed of his past and convinced he is unworthy of connection, he ignores Nadia. His internal life reveals a man haunted by loss: He was a two-time Super Bowl champion quarterback whose career ended after a traumatic brain injury that also left him with a stutter. He developed an alcohol addiction during his playing years and has been sober for years, though he has never pursued formal therapy.
At a family dinner, Tommy pressures Nadia to drink, which she refuses because of her father's alcohol addiction. Griffin quietly shields her from Tommy's pushiness. Griffin hits a stray dog with his truck and rushes it to the clinic, where Nadia helps amputate its leg. She names the dog Tripod, and Griffin adopts the animal. When Billie is hospitalized with a pregnancy complication and placed on bed rest, Griffin gives Nadia riding lessons, insisting she wear a helmet because of his own injury. His stutter recedes in her presence, and their attraction deepens.
Mira sends them to evaluate a lame racehorse whose owner plans to send it to slaughter. The owner leers at Nadia; Griffin intervenes. Nadia breaks down over the horse's fate, and Griffin returns from inside leading the animal, having purchased it for her. On the drive home, they share their deepest vulnerabilities. Nadia's father was violent and had an alcohol addiction; he turned on her at fourteen after Stefan, thirteen years her senior, left for boarding school. She spent years couch-surfing to escape. Griffin explains how his injury destroyed his career and identity. Nadia names the horse Cowboy and begins rehabilitating him at Griffin's guesthouse.
At Neighbor's Pub, where Nadia goes to end things with Tommy, Tommy cruelly identifies Griffin as the "town drunk." Nadia follows Griffin outside, and he reveals he has an alcohol addiction but has not had a drink in years. She holds him without judgment. Griffin kisses her passionately against the wall, then recoils at his roughness and apologizes. Nadia tells him not to cheapen what happened, but Griffin cannot cross the line. She leaves, heartbroken.
Griffin takes Nadia to meet his parents, Joan and Doug Sinclaire, to show her that lasting relationships exist. Joan tells Nadia that Griffin has never stuttered around her, something Joan has never seen with anyone else. Joan warns Griffin he must resolve unfinished business from his past. Frustrated by Griffin's continued resistance, Nadia submits a late application to veterinary school at Emerald Lake.
During a weekend at Griffin's mountain property, Nadia reveals she taught herself to shoot and slept with a gun under her pillow for years to protect herself from her father. That night, Griffin hears Nadia touching herself in a nearby tent and enters, unable to resist. They sleep together for the first time. When Stefan and Mira leave early, Griffin and Nadia spend a night alone. Nadia confesses her fear of repeating her mother's fate by giving up her identity for a man. They make love gently, a first for both in emotional intimacy. While Nadia sleeps, Griffin crosses "Make love" off her to-do list.
After Nadia is accepted to vet school, Griffin tells her he has something from his past he must resolve. On a trail ride, he blurts out that he is in love with her. Nadia drives to his mountain house and demands the truth. He confesses that on the night of his career-ending injury in Las Vegas, still drunk, he married a woman named Tonya in a ceremony he does not remember. Her lawyer sent a marriage license, photos, a demand for money, and a threat to release an alleged sex tape. Griffin has been sending divorce papers for years, but Tonya has finally agreed to sign. Nadia is shaken but tells him she could never hate him.
Back at Gold Rush Ranch, they find Stefan waiting alongside Tonya, who demands more money. Griffin refuses. Stefan is disturbed to learn his sister is involved with Griffin, but Griffin tells Stefan he is in love with Nadia. She scolds both men for centering themselves rather than respecting her autonomy. Stefan gives cautious approval but implores Nadia not to become their mother, who gave up everything for a destructive man. His words strike her deepest insecurity.
Nadia and Griffin agree to a painful clean break. She tells him she needs to prove she can accomplish something on her own and wants him to confront his shame. She does not expect him to wait, though he resolves to do so. Griffin goes to Neighbor's Pub, orders bourbon, pushes the glass away, and calls his father about rehab. He checks into a twenty-eight-day program, undergoing therapy and speech therapy for the first time.
Over the following months, Griffin sends Nadia notes in pale-pink envelopes, each containing a wildflower seed packet with a description linking the flower's traits to qualities he admires in her. Nadia thrives at Emerald Lake, rising to the top of her class. During spring break, a final envelope directs her to "the field where I fell," the property where Griffin first told her he loved her. She finds the field planted with wildflowers from his notes. On the hilltop stand a new barn, white-fenced paddocks with Cowboy grazing, and Griffin's Airstream trailer. At the gate hangs a hand-carved sign: "Wildflower Racehorse Rescue." Griffin tells her the property is hers regardless of whether she wants him. Nadia tells him she loves him for the first time, saying she can do anything without him but does not want to.
In the epilogue, set three years later, Griffin attends Nadia's veterinary school graduation and surprises her with plane tickets to Costa Rica, the tropical vacation from her list, where he proposes. A final flash-forward shows Nadia pregnant at their annual Costa Rica trip, Griffin proposing again as he does every year though they are already married. Nadia reflects on the peace and belonging she has found, a life she never dared to imagine.