At a modern nursing home, an elderly man named Duke reads a heartfelt romantic tale from his notebook to a female patient.
The story unfolds in 1940 at a lively carnival on Seabrook Island, South Carolina, where a young lumber mill worker, Noah Calhoun, first lays eyes on Allison "Allie" Hamilton, a 17-year-old heiress enjoying her summer. Despite being from different worlds, Noah pursues her and eventually wins her affection, igniting a passionate romance.
As the story progresses, Allie's initial connection with Noah's father, Frank Calhoun, is favorable, but the disapproval of her own parents casts a shadow over their relationship. One evening, Noah takes Allie to the abandoned Windsor Plantation, sharing his dreams of restoring it. As dusk descends, their intimacy grows, but their moment is cut short when Noah's friend Fin interrupts, cautioning them about Allie's anxious parents searching for her.
Back at her mansion, Allie's mother, Anne, sternly forbids her daughter from seeing Noah, pushing Allie to impulsively break off their relationship, a decision she quickly regrets. The following morning, Anne announces the family will return to Charleston, prompting Allie to seek Noah. However, her attempts to apologize are in vain, leading her to ask Fin to convey her love. Sadly, Noah arrives too late to reconcile.
Heartbroken, Noah writes to Allie daily for an entire year, but her mother intercepts each letter. When Allie provides no reply after 365 days, Noah gives up hope and enlists in the military alongside Fin, who tragically dies during the Battle of the Bulge. Meanwhile, Allie becomes a nurse, where she meets Captain Lon Hammond Jr., a charming young lawyer from a wealthy family. Eventually, they become engaged, much to her parents' satisfaction.
After the war, Noah discovers that his father has sold their family home to finance the restoration of the Windsor Plantation, which Noah believes will bring Allie back to him. Upon completion, he refuses to sell the property, and while Allie tries on her wedding dress, she sees a photograph of Noah in front of the beautifully restored house and faints, stirring long-buried emotions within her.
Driven by her rekindled feelings, Allie decides to take a trip alone before the wedding. Upon returning to Seabrook, she finds Noah in their dream home, where they passionately reconnect. Allie learns of the letters Noah wrote, realizing her mother had hidden them away from her all this time.
However, the peace is fleeting as Anne arrives to caution Allie about Lon's presence in Seabrook and reveals her own past of love with a lower-class man, urging Allie to choose wisely. An intense argument ensues between Noah and Allie, pressuring her to contemplate her desires rather than societal expectations. Left sobbing and conflicted, Allie confesses her emotional betrayal to Lon, who still wishes to reconcile. Ultimately, driven by her heart, she chooses to return to Noah.
In the present day, we learn that the elderly woman Duke has been reading to is actually Allie, now facing the challenges of dementia. Duke, whose true identity is Noah, uses a different name not to alarm her. The journal he shares with her was penned during her early illness stages, chronicling their love story and life journey to anchor her memories. Almost at the journal's end, Allie inquires about the story's conclusion, and Noah encourages her, reminding her she already knows it. For a fleeting moment, she recognizes him, asking how long their connection will last before slipping away again. Duke manages to comfort her, revealing they may have only five more minutes together.
As they dance to their cherished song, "I'll Be Seeing You," Allie, still seeking remnants of their children, finds joy in the moment. However, her fragile grasp on reality quickly fades, leading to panic at the touch of a stranger, and she is sedated. Later, Duke suffers a heart attack but, despite being restricted, sneaks into Allie's room where she immediately recognizes him. They share a tender kiss and drift off holding hands, only to be found peacefully passed away together, united in everlasting love.
