I love this movie. It's fairly old now, made in 1987, with Theresa Russell and Debra Winger. But the plot is quite unusual and the outcome of the movie made it worthwhile. No movie ends as well as The Sixth Sense (M. Night Shamalian did a hell of a job on that movie!) but this one was still very satisfying.
The Black Widow centers around Theresa Russell, who plays several women who are young, beautiful, have no family and marry very rich men. She does thorough research, not just knowledge of new topics but new wealthy men as well. She manages to avoid having her photo taken as much as possible, and over the years, develops a new look to go with her new life.
(The image above was taken by me at last year's Hallowe'en Chiller Theatre's Convention in Parsippany. This is 31 October 2011; the movie is from 1987, so she looks a lot younger in the film.)
The trail begins to appear over months and is noticed by Debra Winger's character. At first she is looking for a connection to Mob dons who are showing up dead, but then her interest shifts to two men, dead a year apart, both middle=aged, richer than God and both dead of something called Ondine's Curse, a mysterious death that happens to seemingly healthy middle-aged men who die in their sleep. When a third man shows up dead of the same thing ten days prior, then Debra's character begins to look at the wives... a woman who seems to avoid the cameras and looks different in each marriage, but whom Debra thinks is the same person.
It wouldn't be fun to give away the rest, but it is an easily found movie and undoubtedly on Netflix. See it if you get the chance.