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…