Tom Baker (Steve Martin) and his wife, Kate (Bonnie Hunt), take their children for what they hope will be a relaxing summer at a lakeside resort. When the Bakers end up with the shoddiest unit imaginable, a clueless but well-meaning Tom struggles to repair it himself. To make matters worse, Tom's old nemesis -- Jimmy Murtaugh (Eugene Levy) -- and his similarly gigantic family appear on the scene and engage the Bakers in a not-so-friendly rivalry that threatens to spoil their trip.