Gaslight (1940)

Twenty years ago, old Mrs. Barlow was killed in her home at 12, Pimlico Square for her priceless rubies. The murderer searched the whole house without finding them, then disappeared. The house has been empty since then, but now Paul and Bella Mallen move into the apartment. Bella Mallen suffers from forgetfulness and nervousness - at least that is what her husband tells her. An elderly horse wrangler, B.G. Rough worked as a policeman twenty years ago and still remembers the unsolved case. He notices that Mr. Mallen looks just like Louis Barre, Mrs. Barlow's nephew. And why does Mr. Mallen so mysteriously leave every night just to go into the apartment next door, nr. 14?