On their way to Monte Carlo, Monaco, Marilyn and her husband, Neil, meet several other married couples, including Julian and Phoebe, 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 is determined to track them all down.

Medical-center doctors discover the shocking source of a deadly virus spreading through Los Angeles.