While exploring the historic town of Louisburg in Nova Scotia, Canada, freelance writer Margot has an unexpected encounter with Daniel, an artistic rickshaw operator. Their paths cross again on a flight from Halifax to Montreal, and subsequently to Toronto. Upon returning home, they share a cab ride, during which a palpable attraction develops between them. Margot discovers that Daniel actually resides across the street from her, and before they part ways, she feels compelled to remind him, >“I’m married."
Margot has been married to Lou for nearly five years. Their relationship has become comfortable, albeit somewhat uninspiring, yet their feelings for one another remain sincere. Lou is fiercely dedicated to his work on a cookbook, and the couple enjoys a close bond with Lou's family. Among them is Geraldine, Lou's sister and Margot's best friend, who is a recovering alcoholic.
However, as Margot and Daniel continue to spend time together, she opens up about her insecurities and writing aspirations. During a day of casual drinking, Margot jokingly tells Daniel that she plans to kiss him in the year 2040 at the Louisburg lighthouse, a tribute to their playful banter about her faithful marriage. Though Daniel is frustrated by Margot's marital status, he refrains from any physical intimacy.
On the night of Margot and Lou’s anniversary, Daniel offers to transport them on his rickshaw to their dinner, which Margot declines. Ignorant of any underlying tension, Lou eagerly accepts his friend’s offer. As time goes on, Margot and Daniel's bond deepens, which includes a silent moment in a pool and a day of joy at an amusement park. When Margot enters Daniel's home and sits beside him on the bed, she finds herself overwhelmed by guilt and leaves before they can act on their feelings.
As Margot and Lou celebrate Geraldine’s sobriety at their home, Daniel initially declines Lou's invitation but eventually agrees to join the festivities. Witnessing the connection between Margot and Lou makes him despondent. When Margot confronts him about his sadness, Daniel reveals his frustration with her indecision and makes it clear he doesn’t wish to be a contender in a love triangle. Accepting that this tumultuous relationship will only lead to heartache, he abruptly moves out, leaving Margot a postcard from Louisburg that reminisces about their plans for the year 2040.
Margot then awakens from a vivid dream of a passionate kiss with Daniel, compelling her to tell Lou she wants a divorce. Soon, the two lovers find each other again and express their feelings physically. Unfortunately, life takes a somber turn when Margot receives troubling news about Geraldine, who has gone missing. She rushes back to console Geraldine's daughter. In a heated moment, a drunken Geraldine chastises Margot, revealing her own struggles and claiming that Margot's betrayal—for an illusion of happiness—was even more grievous. After Geraldine opts to face the law for her DUI, Margot and Lou share a poignant farewell.
As time moves forward, Margot and Daniel adapt to a new routine that bears a resemblance to her previous life with Lou. Even though Daniel holds affections for Margot, the fervor that once ignited their relationship seems to have dulled. The narrative concludes with Margot riding alone at the amusement park, a symbol of her solitude amid the choices she has made.
