It's 1876 and Leopold (HUGH JACKMAN), the third Duke of Albany, is a charming and handsome aristocrat who's been brought to New York in hopes of marrying him to a young socialite from a wealthy family. A man of fine standards who's also an inventor, Leopold is intrigued by his repeated sightings of Stuart (LIEV SCHREIBER), a man who doesn't seem to fit in with his surroundings.
Racing after him one night trying to learn who he is and what he wants, Leopold suddenly find himself, along with Stuart, transported through a time portal into present day New York. Leopold is obviously shocked by his new surroundings, and learns that it was Stuart who discovered the rip in the fabric of time that's allowed their travel.
As he quickly becomes accustomed to this new world, Leopold meets Kate McKay (MEG RYAN), Stuart's ex-girlfriend and a marketing executive who still lives one floor down from Stuart. Cynical about men after a failed four-year romance with Stuart, Kate doesn't believe his or Leopold's accounting of what's happened. Her out of work actor brother, Charlie (BRECKIN MEYER), believes Leopold to be a convincing, if nonstop thespian.
With Stuart hospitalized after a fall in the elevator, Kate gets to know Leopold and is eventually won over by his charming, debonair, and decidedly old-fashioned ways. In turn, he finds himself falling for her, even though he doesn't necessarily agree with her profession. As she tries to land a promotion from her boss, J.J. (BRADLEY WHITFORD), with the aide of her assistant, Darci (NATASHA LYONNE), Kate must decide what to do about Leopold who Stuart needs to return to the 19th century in less than a week.