Set against the backdrop of the charming fictional town of Thayer in New England, the film revolves around Everett Stone and his exceptionally close-knit family. His girlfriend, Meredith, portrayed as anxious, awkward, and tightly wound, is filled with dread at the thought of spending the Christmas holidays with Everett's family.
As Meredith navigates this tight family dynamic, she finds herself perceived as an outsider. The rest of the family, reacting at first with discomfort and then with sternness to her stiffness, only amplifies her feelings of alienation. However, Ben, Everett's brother, seems to take a liking to her. After a series of cringe-worthy moments, Meredith decides to check into a local inn and pleads with her sister Julie to come down on a bus for moral support. When Julie arrives, she is greeted with warmth by Everett's family, especially after a comedic incident where she stumbles while disembarking from the bus.
Meredith makes desperate attempts to integrate with the Stones, yet her efforts continually backfire. During a family dinner, the conversation shifts to a topic about adoption, prompted by Everett's gay, deaf brother Thad and his partner Patrick. When Meredith clumsily tries to contribute to the discussion, her poor word choice offends everyone, leading to an explosion of emotions where even Everett's father Kelly, usually the most understanding member, sternly shuts her down. Feeling hurt and cornered, Meredith tries to leave in a flurry of overwhelming emotions, resulting in an unfortunate car crash with Everett's vehicle. It is at this moment that Ben comes to console her, revealing a budding attraction towards Meredith, which leads to a night out at a bar. After a few drinks, Meredith starts to unwind and even invites local paramedic Brad Stevenson, who was Amy's high school sweetheart, to join them for Christmas breakfast. The next day, chaos ensues as she wakes up in Ben's bed, mistakenly believing the two had spent the night together.
On Christmas Day, the Stone siblings receive harrowing news about their mother Sybil—a breast cancer survivor who now faces a serious recurrence of the disease. Although she initially refuses Everett's request for his grandmother's ring, which he intended to use for proposing to Meredith, she later has a change of heart. In a twist of fate, Everett, now with growing feelings for Julie, asks her to try on the ring, causing it to get stuck on her finger. This leads both sisters to think that Everett is about to propose to Meredith when they lock themselves in the bathroom trying to remove the ring.
As gifts are exchanged, Meredith, blissfully unaware of Sybil's deteriorating health, presents each family member a framed photograph of Sybil taken during her pregnancy with Amy, thinking it features Sybil with Everett. The gesture resonates deeply with everyone, softening Meredith’s tension. However, when Everett seeks a private conversation with her, she impulsively declares her refusal to marry him, to which he responds that he hadn’t intended to ask in the first place. This moment sets off an emotional breakdown for Meredith in front of the family, leading to a cathartic resolution for everyone involved as they begin to heal through their conflicts.
Fast forward one year, and the Stones gather once again for Christmas. Now, Meredith and Ben are together, while Everett is with Julie. Additionally, Amy and Brad are a couple, and Thad and Patrick have joyously adopted a baby boy named Gus, along with Susannah, who has welcomed another son named Johnny. The shadow of Sybil’s passing looms over the family gathering, yet they come together under the Christmas tree, cherishing her memory.
