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

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.