During World War II, allied soldiers Ralph Bates and Yves Beneyton escape from a Nazi POW camp in France. They escape to Lyons, where they accept the hospitality of mademoiselle Cherie Lunghi. The woman has a psychic sister, played by Mathilda May, who sees dark days ahead for the two escapees. Sure enough, Bates is killed, whereupon Beneyton, at Lunghi's behest, assumes Bates' identity. It's all part of a complex inheritance-scam plot, but Beneyton does not figure this out until he's in too deep. Letters to an Unknown Lover is based on the Boileau-Narcejack suspense novel Les Louves, which was the original French title of this film.
~ Hal Erickson, All Movie Guide