Jack Sadelstein, a successful advertising executive in Los Angeles, leads a comfortable life with his beautiful wife, Erin, and their two children. Despite his seemingly perfect world, there is one annual event that he dreads: the Thanksgiving visit of his identical twin sister, Jill. Jill's neediness and passive-aggressiveness cause great stress for Jack, who feels increasingly exasperated by his sister's presence. Her visit stretches beyond the holiday, exacerbating the tension as Jill interferes with Jack's personal and professional life, her eccentric behavior challenging the patience of everyone around her.

In an effort to win a prestigious advertising account, Jack attempts to convince legendary actor Al Pacino to participate in a commercial for the Dunkin' Donuts Dunkaccino campaign. Unexpectedly, Pacino becomes smitten with Jill, her overt peculiarities notwithstanding. Jack sees an opportunity to leverage Pacino's infatuation and encourages Jill to spend time with the actor, hoping that it will seal the deal for his campaign. However, Jill's experiences in the world of Hollywood and with Pacino prove to be much more complicated than Jack anticipated, leading to a series of misadventures that force both siblings to reevaluate their relationship and what truly matters in their lives.