ID an old movie

It’s an old black and white movie, I think it was set sometime after WWI.

A wealthy British (possibly American?) woman lives in her family’s large Italian(?) villa. Her brother, presumed dead in a car accident, returns home, only it’s not her brother. She summons a detective from the local police and the brother spends the better part of the evening trying to convince them both that he is, in fact, her brother. The “brother” seems to know everything about the woman and the family that he should know, and eventually convinces the detective and he leaves.

The woman remains certain that he is not her brother, and begins to question her own sanity as mysterious events continue to unfold…

I won’t give away the rest in case this interests anyone who wants to see it (I really enjoyed this movie), but I think that should be enough to ID this movie. If not, I can go on. The title is just completely escaping me.

Chase a Crooked Shadow?

Yes! Thank you. All I could remember of the title was “Shadow” and that was getting me nowhere.

If I can just piggyback on this thread rather than take up space with another… I have been trying to ID a movie for a number of years (not trying very hard, just keeps bugging me).

The only scene I can remember is the vaguely James Bondian type (Rock Hudson? Tab Hunter? Rod Taylor?) in the hands of the gang of bad guys. It’s an outdoor scene in a sort of old English farm or village setting. The salient dialogue is about the girl, of course - Our Hero wants to know where she is, and the leader of the gang says something like “She’s with [boss name]. Maybe they’re doing the same thing… together!” At which point Our Hero goes predictably nuts, shouts threats, etc.

Anyone recall that scene and line of dialog, and thus movie?