This is a film about what is sometime called (or was sometimes called) female cunningness but I think that expression is somewhat biased from a male point of view. What happens in this film between different persons - this time a woman being the instigator - could of course just as well been the work of a man.
Joan Fontaine is Christabel, a woman coming to live with her cousin Donna (Joan Leslie).
Having installed herself there, she starts to flirt with Donna's fiancée, the wealthy Curtis (Zachary Scott) but she does so in a way making her look like a innocent victim of circumstances.
She fools Curtis to believe that it's her cousin Donna who wants his money while it's the opposite, of course.
When having outmanoeuvred Donna, she marries Curtis but only for his money as she's actually in love(?) with Nick (the fine actor Robert Ryan). He also loves her but on the same time he despises her for what she has done and for what she is.
This is no masterpiece when it comes to the idea and the very cliché-filled story and plot, implying that one describes the individuals as either being 'this way or that way'. The acting is mostly good but sometimes the American 'over-explicitness' tends to annoy us, gazes, blinks etc. in order to make the American audience fully understand the different twists of the story. The main actors - Joan Fontaine, Robert Ryan and Joan Leslie - lifts the story above the mediocre.