Abby Holland and Harper Caldwell are a couple who have been dating nearly a year. Abby has disliked Christmas since her parents passed away, so Harper spontaneously invites Abby to celebrate the holidays with her family in her hometown. Abby sees this as the perfect opportunity to introduce herself to Harper’s parents and propose to her on Christmas morning. However, on their way to the Caldwells’ house, Harper reveals she lied to Abby about coming out to her parents previously; fearing doing so would interfere with her father’s campaign for mayor, she doesn’t want to come out to her family until after Christmas. She asks Abby to pretend to be her straight roommate for the holiday, to which Abby reluctantly agrees.
At the Caldwells’ house, Abby meets Harper’s father, Ted, her perfectionist mother, Tipper, and her wacky artistic sister, Jane. The family welcomes Abby as Harper’s “orphan friend” who has nowhere else to go for Christmas. Abby becomes uncomfortable, especially when she meets Harper’s exes, Connor and Riley. During the visit, she begins questioning how much she knows about her girlfriend when she sees Ted and Tipper’s high expectations and Harper’s competitive relationship with her older sister, Sloane.
Ted is trying to impress a possible donor from the city council to contribute to his campaign, which Abby unwittingly jeopardizes when Sloane’s children put an unpaid-for necklace into her bag during an outing to the mall. Believing she is a shoplifter, Ted and Tipper think it might be better if they keep Abby away from upcoming social events. From this point, Abby feels even more like an outsider. She also learns from Riley that Harper has publicly denied her sexuality ever since she was a high school freshman, which makes Abby worried about the future of their relationship.