During a wild vacation in Las Vegas, career woman Joy McNally and playboy Jack Fuller come to the sober realization that they have married each other after a night of drunken abandon. They are then compelled, for legal reasons, to live life as a couple for a limited period of time. At stake is a large amount of money.

What Happens in Vegas has a few laughs, but mostly settles for derivative romantic comedy conventions and receives little help from a pair of unlikable leads.