Classic crime drama film title help

This is what I can remember.

A younger man with a past is hired to go work for a rich man and his wife (on an island or plantation or tropical mining operation). This rich man is a bit older and is sick. His wife is young and beautiful. He has some sort of very large and valuable jewel or priceless object in his house that is in some sort of glass case with special access and crazy security alarms etc attached. The younger guy and the rich man's wife are subtly attracted to each other and she secretly suspects him of being there so steal the jewel. From what I remember they both plan to steal it and of course things don't go as planned. This is where I don't remember the rest.

If anyone has any ideas I would be very thankful.  Thanks everyone!