When a cynical US President suffers a near fatal heart attack while in the arms of his mistress, a small town lookalike, the genial Dave (Kevin Kline), is called upon to act as his double. The doppelganger brings an innocent vitality to his new job, and begins to call the shots, much to the displeasure of the power hungry politician who intends to use him as his stepping stone to the Presidency. Meanwhile, the President's wife (Sigourney Weaver) is at first suspicious and then charmed by the unexplained transformation in her estranged husband's character.