The Hidden Room (1949)

London psychiatrist Clive Riordan, royally fed up with the repeated affairs of his wife Storm, plots a seemingly 'perfect' revenge against her latest lover, American Bill Kronin. Catching them in the act, he marches Bill off at gunpoint; and from the viewpoint of Storm and the rest of the world, Bill simply vanishes.

But there's far more to the meticulously worked out plot than Clive's victims suspect, with the end slowly preparing in his private laboratory. Enter a mild-mannered Scotland Yard man, who seemingly has no clue beyond a missing dog.