Mia Landan, a 38-year-old breast cancer survivor and former public relations director in Charleston, South Carolina, arrives at a remote cabin in the North Carolina mountains during a rainstorm. Her sister, Madeline, signed her up for a Casting for Recovery retreat, a three-day fly-fishing program for breast cancer survivors led by guide Belle Carson. At the retreat, Mia felt a spark of hope for the first time since her mastectomy and chemotherapy. She drove home early to surprise her husband, Charles, a lawyer, only to find him in bed with another woman. She fled without confronting them, and Belle found her sobbing at the deserted retreat site.
Belle offered Mia refuge in a cabin she inherited from her late mother, Theodora, who had inherited it from her own mother, Kate Watkins. Abandoned for years, the cabin lacks phone service, central heat, or hot water. Mia insists on staying, arguing she has lost her breast, her hair, her job, and her husband. They agree she will stay rent-free for the summer in exchange for cleaning the place.
Mia throws herself into scrubbing the filthy cabin, finding the labor therapeutic. She discovers a locked armoire containing hand-painted china, sterling silver engraved KW, a blue taffeta gown, and bamboo fishing rods, possessions suggesting a woman far more refined than expected. In the nearby town of Watkins Mill, locals tell her Kate Watkins allegedly killed her lover and that the cabin is considered haunted. Kate's daughter, Theodora, left town as a teenager and never returned. Mia begins painting watercolors of the river and one evening looks at her mastectomy scar for the first time, praying for strength to release her fear that the cancer will return.
After accidentally blowing a fuse, Mia searches the bookshelf by flashlight and discovers a leather diary with the gilt initials KW, a childhood journal begun in 1912. Kate's entries reveal a precocious girl who painted wildflowers on her bedroom walls to conquer her fear of the woods, inspired by her father, Reverend Walter Watkins. Mia identifies with Kate's determination and resolves to venture farther into the wilderness each day. Belle stops by with fly-fishing gear, takes the bamboo rods after recognizing one as a museum-quality Payne split cane rod, and asks Mia not to stir up old stories about Kate before departing for a six-week fishing trip in Scotland. Mia then finds Kate's fishing diary: a thick volume spanning 1920 to 1951, filled with exquisite watercolors of rivers, trout, and wildlife. She resolves to uncover Kate's full story.
At the library, Mia traces the Watkins genealogy and meets Phillip Pace, Kate's elderly childhood friend, who insists Kate never killed anyone. He describes her graceful casting style, her disqualification from a tournament for being female, and her nationally syndicated column, "On the Fly." Charles calls demanding a divorce, and Madeline delivers further news: Charles plans to marry Julia Barnes, a law clerk at his firm who is pregnant. Mia is devastated but resolves to focus on healing, establishing a routine of painting, walking, and fly-fishing.
While fishing a backcountry stretch, Mia meets Stuart MacDougal, who is setting up a fly-fishing shop at Watkins Lodge, the resort built on the former Watkins estate. He helps her land her first solo catch, and over the following weeks they develop a quiet companionship that deepens into mutual attraction. At the Gazette, Mia and editor Nada Turner uncover Kate's "On the Fly" columns in the archives, witty essays syndicated nationally in the 1920s. Mia also visits Mrs. Minor, a 92-year-old woman whose mother cooked for the Watkins family, who reveals that Theodore DeLancey, a New York fly fisher, visited Kate twice a year for four years and that they loved each other deeply.
Nada republishes Kate's articles, and the town begins celebrating Kate as a pioneering fly fisher. Stuart discovers Kate's fishing diary at the cabin, and Mia confesses her research; he promises to keep her secret. Through continued investigation, Mia learns there was never a murder trial or a body found. DeLancey was only declared a missing person, the scandal fueled by sensationalist reporters and the accusations of his wife, Camilla. Kate sat silent throughout the investigation, never defending herself. Mia also learns that Theodora, stigmatized as the daughter of a woman accused of murder, fled at 17. Kate searched for her for years and eventually drowned in the river.
At Watkins Lodge, Mia and Stuart find Kate's initials on unsigned oil paintings. Hidden behind the frames are a stanza from Dante's
Inferno about the doomed lovers Paolo and Francesca, a photograph of DeLancey, and a love letter in which he calls Kate his Francesca. Overwhelmed, they make love for the first time, Mia's fear of revealing her scarred body dissolving as Stuart holds her gaze without flinching. Madeline visits and is amazed by Mia's transformation. Charles offers to buy Mia's half of their condominium; she accepts and signs the divorce papers without hesitation.
When Mrs. Minor dies, her granddaughter gives Mia a sealed letter Kate wrote to Theodora, entrusted to Mrs. Minor for delivery decades earlier. Mia refuses to open it. Belle returns from Scotland furious that Mia investigated despite being asked not to. Mia gives Belle all the diaries and the sealed letter. Belle orders Mia to leave after the storm passes. Devastated, Mia seeks refuge with Stuart. But during the hurricane, Belle returns transformed, having read the diaries and the letter. She gives the letter to Mia, saying she deserves to know the ending.
Kate's letter reveals DeLancey came to the cabin in November 1929, desperate after losing both their fortunes in the stock market crash. Kate was pregnant but chose not to tell him. At dinner, DeLancey said he could not face the diminished life ahead, invoking their shared Dante allusion to doomed love. Kate understood he was contemplating suicide. Repelled and enraged that he would abandon her and their unborn child, she threw her locket at him and left. She waited at the cabin all night, and late that night she felt his presence and knew he was dead. Kate kept silent for decades to protect his family: Had she voiced her belief that he died by suicide, the insurance company would have denied the payout they needed.
The hurricane triggers mudslides, and bones are found in debris on Route 9. Mia connects this to Kate's letter, which described a mudslide destroying that same road the night DeLancey vanished. She theorizes DeLancey was walking through the storm to reach Kate when the slide buried him. Mia and her allies present the evidence to the sheriff, who requires DNA from a blood relative. Belle steps forward: Kate's unborn child became Theodora, making Belle DeLancey's granddaughter. She offers her DNA. Tests confirm the bones are DeLancey's, and the coroner rules his death accidental, ending nearly 80 years of scandal.
As autumn arrives, Mia closes the cabin. She no longer senses Kate's presence; whatever held Kate's spirit has been released. Belle fastens around Mia's neck the gold locket found clutched in DeLancey's hand, proof he carried it through the storm to reach Kate, and tells Mia the cabin will always be her room. Stuart tells Mia he will be waiting when she returns from Charleston, where she must finalize her divorce and see her doctors. In a final walk to her favorite spot, Mia ties her own fly, catches a brook trout, removes the hook herself, and releases it. Standing in the current, she feels a timeless connection to the water and all living things. She dips her hand into the river and whispers, "Remember me." She is a survivor.