Drew Latham (BEN AFFLECK) is a wildly successful marketing executive in Chicago who'd like to go to Fiji with his girlfriend, Missy Vanglider (JENNIFER MORRISON), over Christmas. Upset that he'd rather do that then spend the holidays with family -- especially his that she's never met -- Missy dumps him, leaving Drew in a quandary when no one will invite him to share their holiday festivities.
Following some advice to make a list of personal grievances and then burn them at some place from his past, Drew tries to do just that at his former childhood home. Unfortunately for him, the current owner, Tom Valco (JAMES GANDOLFINI), thinks he's an arsonist and knocks him out with a snow shovel. When Drew comes to, he offers Tom, his wife Christine (CATHERINE O'HARA) and their 15-year-old son Brian (JOSH ZUCKERMAN) an offer they can't refuse.
In exchange for allowing him to move in with them through Christmas and have them act like his family, he'll pay them $250,000. They reluctantly agree but make him pay more for a local actor (BILL MACY) to play the family's grandpa, "Doo-Dah." Things become more complicated when adult daughter Alicia (CHRISTINA APPLEGATE) arrives for the holidays and is none too happy to see that her family has let a seemingly eccentric man move in with them, money or no money.
As the days progress toward Christmas and the Valco family dynamics finally come to the forefront, Drew hopes to have the happy holiday extravaganza about which he's always dreamed.