Secret Beyond the Door (1947)

I rather enjoyed this film - Fritz Lang leaves much of the intrigue to emanate from own imagination. "Celia" (Joan Bennett) meets and quickly falls in love with Michael Redgrave ("Mark"), an enigmatic gent from a family that has known better days. They decamp to his remote family mansion where she meets his sister, and his teenage son - of whom she was hitherto unaware. Things all start to take a turn for the strange once she arrives; her husband collects "rooms" - he recreates the rooms where historically macabre events have happened. There is a room in their home that he keeps locked - what's inside? Her paranoia, fuelled by some eerily lit scenarios and a good, suspicion-arousing performance from Redgrave gradually builds into quite a tense denouement. It has shades of "Rebecca" (1940) about it - the sister "Caroline" (Anne Revere) assuming the role of the mysteriously obsessive third party and there is enough ambiguity going on to keep it interesting until the end.