Janet Graham is a successful businesswoman who has distanced herself from her family due to their eccentricities and chaotic gatherings. However, Janet feels guilty for not spending time with her family, and decides to attend their annual spring-time Christmas celebration.
As soon as she arrives, she realizes that not much has changed. The family's home is decorated with Christmas lights, ornaments, and tinsel, while the smells of gingerbread and peppermint fill the air. Janet's mother, father, and siblings seem to have embraced their oddities, with her father dressed as Santa Claus, her mother speaking in riddles, and her siblings dressed in Christmas-themed costumes.
Despite the chaos, Janet enjoys spending time with her family, until she discovers her father's lifeless body in a nearby shed. When she tries to call the police, her family asks her to wait until after the holiday celebrations to avoid ruining the festivities. Janet becomes the prime suspect and must find the real murderer before the police arrive.
As she begins her investigation, she discovers clues that lead her to believe that someone in her family may be the killer. She also learns about the family's odd traditions, including their "Snowman Wars" competition and their annual "White Elephant" gift exchange, where family members bring the strangest and most useless items to swap.
Despite the time pressures, Janet manages to attend the family's bizarre nativity play while gathering more clues. When the police show up earlier than expected, Janet must use old home movie footage, which captures the murderer in the background, to prove her innocence and solve the mystery.
Throughout the movie, Janet finds a way to connect with her family and learn to embrace their quirks and traditions.