A Caribbean Mystery (movie, 1983)

Aging Major Palgrave, an idiosyncratic but charming mystery writer, reveals to Miss Marple that one of the guests at a luxurious Caribbean resort they're staying at is a Bluebeard-type wife murderer. Unfortunately, the Major succumbs to an apparently accidental overdose of alcohol and blood pressure medication before revealing the killer's identity. When it's discovered that the medicine belonged to another guest and the revealing photograph the Major was carrying is missing, Miss Marple realizes that the serial killer has struck again and more murders will follow.