Jack Sadelstein (Adam Sandler), a successful advertising executive in Los Angeles with a beautiful wife (Katie Holmes) and children, dreads one event each year: the holiday visit of his identical twin sister, Jill (also Adam Sandler). Jill's neediness and passive-aggressiveness are maddening to Jack, turning his normally tranquil life upside down. Things spin even more out of control for Jack when Jill decides to extend her visit--and he doesn't think that she'll ever leave.