Italian title: In fondo alla piscina
English title: The Fourth Victim
Eugenio Martín
The police suspect that the rich Mr. Anderson, a three-time widower, killed his wives to get hold of their insurance. But there's no evidence against him and now he's getting married for the fourth time. However the new slyly wife is the sister of one of the deceased who, in disguise, intends to concoct a plan to unmask him.