On their way to Monte Carlo, Monaco, Marilyn (Cybill Shepherd) and her husband, Neil (James Belushi), meet several other married couples, including Julian (Richard Lewis) and Phoebe (Sean Young), who are traveling with a lost dog they plan to return to its wealthy owner for a large reward. But, when the dog's mistress is murdered, the travelers become the prime suspects, and Inspector Bonnard (Giancarlo Giannini) is determined to track them all down.