Pete and Mac take an ocean cruise to get Harmon, a fellow passenger (Lloyd Bochner) to admit that he had his bookkeeper murdered. All the action takes place in Puerto Vallarta.

A syndicate don helps turn the tables on Jean Paul Jacquard, a swindling French Romeo (Ricardo Montalban).

A routine investigation of a wealthy man's prospective son-in-law stirs up a storm of violent reaction. This routine background check turns dangerous for Pete and Mac when local police, the FBI and the mob all want to stop their investigation.