Brad (VINCE VAUGHN) and Kate (REESE WITHERSPOON) have been dating for three years, but have no intention of ever getting married or having kids, what with how their respective, divorced parents and families turned out. In fact, they so dislike the thought of getting together with them that not only have they not met the other's families, but they also travel abroad over the holidays to avoid any such get-together, lying that they're bound by charitable work.
When their flight to Fiji is canceled, however, and they end up on the TV news as just one of many stranded holiday travelers, their respective parents call and demand a holiday visit. Their first stop is to see Brad's redneck dad, Howard (ROBERT DUVALL), and his two other sons, Denver (JON FAVREAU) and Dallas (TIM McGRAW), who are amateur ultimate wrestlers. All of them view Brad as being an elitist and do their best to put him in his place.
Next up is a visit to see Kate's mom, Marilyn (MARY STEENBURGEN), and sister, Courtney (KRISTIN CHENOWETH), among others there, who delight in telling Brad embarrassing stories about his live-in girlfriend's past. That is, when they don't attend church presided over by Marilyn's new boyfriend, Pastor Phil (DWIGHT YOAKUM), where the young couple is volunteered to play Joseph and Mary in the Christmas pageant.
That's followed by a trip to see Brad's mom, Paula (SISSY SPACEK), who's now involved with his former best friend from their childhood, Darryl (PATRICK VAN HORN), and then a visit to see Kate's dad, Creighton (JON VOIGHT), who's come to realize the error of his previous ways and the importance of family. As they make their way from one get-together to the next, Brad and Kate come to realize that perhaps they don't know each other as well as they thought they did, and now have different expectations regarding their future together.