It's Christmas time. Kara Gentry's wealthy grandfather, Bob Gentry, who's been estranged from her father, his son Jeff, has telephoned for the first time in years, asking Kara to spend Christmas with him and her grandmother Elsa. Jessie Wilkins has been living with her Aunt Jenny since her mother's death that year--her father having never been in the picture for some unknown reason-- when her paternal widowed grandmother Judy whom she's never met, invites her to spend Christmas with her. Kara and Jessie, both 15, meet on the same Burlington, Vermont to Stillwater, Oklahoma flight, become fast friends, and learn of each other's Christmas plans--and that both are dreading them. When they learn that both are heading to the small town of Guthrie, they decide to switch places so that Kara can experience a Christmas with a more real person than what she thinks her grandparents will be like, while Jessie experiences a Christmas with all the creature comforts unlike how she was raised and unlike how she expects Grandma Judy to be. In and out in one week, no one gets caught, no one gets hurt. They are both able to pull off the ruse as their respective grandparents only know the basics of their lives. But as the week progresses, things get more and more complicated on both sides, as despite their web of lies they have somehow built a certain sense of family with people who aren't their families.