On Christmas Eve, Megan and Kiera are awakened that night by a noise on the roof. While investigating, Megan startles Mrs. Claus, who falls off the roof and dies. Her body vanishes, leaving behind a red suit and business card stating that if anything were to happen to her, someone should put on the suit and the reindeer will know what to do. Megan and Kiera find Santa’s sleigh and reindeer on the roof. At Kiera's request, Megan reluctantly dons the suit and spends the rest of the night delivering gifts before the reindeer take them to the North Pole.
They discover that Megan is subject to a legal technicality known as "the Mrs. Clause," and has accepted all of the late Santa's duties and responsibilities. The head elf, Annette, gives Megan 11 months to get her affairs in order before reporting back to the North Pole on Thanksgiving. Overwhelmed, Megan changes into pajamas provided to her and falls asleep.
Over the next year, Megan undergoes a drastic change; she gains a massive amount of weight and develops an increased fondness for sweets, particularly milk and cookies. Her hair rapidly turns white in spite of attempts to dye it. During a pitch meeting, Megan is angered at a proposal to make a teen soap opera about Mrs. Claus. Megan also begins to recount 'naughty' and 'nice' children by name when she sees them.
