Chicagoan Chester "Chet" Ripley (John Candy), his wife, Connie (Stephanie Faracy), and their two sons, Buckley "Buck" and Ben, are on vacation at a lake resort in Pechoggin, Wisconsin during the summer. All is going as planned until Connie's sister, Kate (Annette Bening), her investment broker husband, Roman Craig (Dan Aykroyd), and their twin daughters, Mara and Cara, crash the vacation.