Abby Holland, portrayed by Kristen Stewart, and Harper Caldwell, played by Mackenzie Davis, are a couple who have been happily dating for almost a year. However, Christmas brings back painful memories for Abby, as she lost both of her parents a few years prior. In a gesture of love, Harper invites Abby to spend the holidays with her family in Pittsburgh, hoping this festive occasion will be an opportune moment for Abby to meet her parents and for Abby to propose on Christmas morning.
As they make their way to the Caldwell household, Harper confesses to Abby that she hasn't come out to her parents yet, fearing that revealing her sexuality might complicate her father's mayoral campaign. In an effort to appease her family, she convinces Abby to pose as her straight roommate during their visit, a request that leaves Abby feeling uneasy but she obliges.
Upon arrival, Abby meets Harper's well-meaning yet demanding father, Ted (Victor Garber), her meticulous mother, Tipper (Mary Steenburgen), and her quirky younger sister, Jane (Mary Holland). The family welcomes Abby as Harper's "orphan friend" in need of a place to celebrate Christmas. However, the situation grows tense when Abby encounters Harper’s past relationships, including her ex-boyfriend, Connor (Jake McDorman), and her ex-girlfriend, Riley (Aubrey Plaza).
As Abby navigates the intricacies of Harper's family dynamics, she begins to question how well she truly knows her girlfriend, especially amid high expectations from Ted and Tipper and Harper’s competitive bond with her older sister, Sloane (Alison Brie). The situation escalates when a misunderstanding leads to Abby being suspected of shoplifting, further isolating her from the family.
At the annual Christmas Eve gathering, Abby is finally relieved when her friend John (Dan Levy) shows up unexpectedly to rescue her. Despite their growing connection, their moment is interrupted by Sloane, who threatens to out Harper and Abby. In a shocking twist, Sloane reveals her own marital troubles, leading to a heated confrontation that turns the party chaotic and forces Harper to confront the truth about her sexuality.
Abby, heartbroken, steps outside for a chat with John, where they reflect on their coming out experiences. John’s own painful story reinforces the message that coming out is a deeply personal journey. Realizing the impact of her decisions, Harper finally reveals her truth to her parents, only to face disapproval. However, this moment of honesty encourages Sloane and even Jane to express their long-buried feelings to their parents.
The emotional turning point brings Harper to seek forgiveness from Abby, affirming her deep love and desire for a future together. In a heartfelt moment, they reconnect with a passionate kiss. Ted, after hearing his daughters, expresses regret for the unrealistic expectations placed upon them and makes a pivotal decision regarding his political ambitions, valuing family over reputation.
Fast forward one year, Abby and Harper are now engaged, Jane enjoys success as a bestselling author with her fantasy novel, "The Shadow Dreamers," and Ted has triumphed in his mayoral campaign. On Christmas Eve, the family gathers at a local vintage cinema to watch "It's a Wonderful Life," where Abby and Harper share a loving smile, embodying the spirit of family and acceptance.
