À la veille de Noël, Greg préfère partir en mission d’infiltration que de rester avec sa famille. Pour lui donner une leçon, le Père Noël l’envoie dans le film de Noël préféré de sa fille pour y aider la famille du héros, Richard Silestone, criblée de dettes. Mais un bug dans le sort envoie Richard, à la place de Greg en pleine mission d’infiltration au cœur d’un réseau de trafiquants de drogue. On Christmas Eve, Greg, a solitary and taciturn police officer, doesn't hesitate to leave his daughter behind to go on a mission. To teach him a lesson, Santa Claus decides to grant his daughter's wish: that her father looks like Richard Silestone, the good-natured and heavily indebted family man from the beloved Christmas movie she adores. While Greg is sent into this improbable world, Richard accidentally lands in the real world and both men realize they have no choice but to complete each other's missions to reclaim their respective lives.