Black Widow [1987] Bob Rafelson

When the ambitious federal investigator Alexandra 'Alex' Barnes reads the cases of two wealthy men that have just died and left their fortunes to their younger and younger wives, she suspects that the woman might be the same. She believes that the woman might be killing the millionaires without a trace to inherit their fortunes. Alex travels and tracks down the mysterious female inheritor Catharine Petersen but she finds nothing about her identity. Alex believes that the Catharine might have traveled to Hawai and she takes vacation to follow her instincts. Alex finds and befriends Catharine in the hotel and becomes close to her. When Alex meets Catherine's boyfriend Paul Nuytten (Sami Frey), she has a crush on him. Will her passion for Paul and her friendship with Catharine jeopardize her investigation?