The Man Who Knew Too Much (1934)

Plot: Londoners Bob and Jill Lawrence and their daughter Betty are in St. Moritz where they are partaking in some sporting competitions: Jill is in a skeet shooting contest, and their friend, Frenchman Louis Bernard, is in a ski jumping competition. While Louis and Jill are on the crowded dance floor together at a party one evening, there is small popping noise among all the other noises in the room, that pop which ends up being a gunshot fired at Louis. Just before he dies in Jill's arms on the dance floor, Louis vows her to secrecy as to what he is about to say: that there is a brush in his hotel room - the key to which he slips to her - the brush which she must take to the British consul. Jill confiding only in Bill who takes the key, he is able to find the brush which contains a cryptic note inside the handle. They also find that a man in the skeet shoot competition - who they only know as Ramon - also wants the note in the brush, with he and his associates having kidnapped Betty to get it. The Lawrences are to say nothing to the authorities or they will kill Betty. Back in London without Betty, the Lawrences learn directly from the British Foreign Office that Louis worked for them, his latest case was about an upcoming assassination attempt on a high ranking foreign official, that piece of paper in the brush is probably the key to finding out the assassination plans, and a successful assassination could spark the start of a war. Bill and Jill believe that piece of paper, which they refuse to turn over, is what is keeping Betty alive. As such, the Lawrences have to decide how much investigation to do on their own with their loyal friend Clive, and how much to involve the Foreign Office, in their primary mission to save Betty, with thwarting the assassination a bonus if they are able.