The Amazing Mr. X (1948)

On the beach one night, Christine Faber, two years a widow, thinks she hears her late husband Paul calling out of the surf, then meets a tall dark man, Alexis, who seems to know all about such things. After more ghostly manifestations, Christine and younger sister Janet become enmeshed in the eerie artifices of Alexis, but he in turn finds himself manipulated into deeper deviltry than he had in mind.