Bulldog Drummond's Peril (1938) on Netflix

Plot summary

Captain Hugh "Bulldog" Drummond and Phyllis Clavering plan to marry at her villa in Switzerland, but the policeman guarding their wedding presents is killed. The thief takes a synthetic diamond made by Professor Bernard Goodman through a secret process; Goodman is the father of their friend Gwen Longworth. Sir Raymond Blantyre, who leads the Metropolitan Diamond Syndicate, vanishes at the same time. Drummond suspects the head of the syndicate and returns to England, leaving Phyllis in Switzerland. Colonel Nielsen of Scotland Yard dismisses his suspicions, insisting that so respected a man could not be involved, yet has Drummond watched.