Bulldog Drummond at Bay (1947)

"Bulldog" Drummond is vacationing in his country home in England, and his house if rifled by two thieves. After they leave he finds a card marked with some mysterious letters. Doris Meredith comes by the next day, pretending her car has broken down. Drummond knows better but plays along with her. Drummond calls Scotland Yard Inspector Holmes, and is informed that some of the letters comprise the code-name for a Yard-man who disappeared while carrying some diamonds from France to England. Doris tells Drummond the man is her brother. Drummond uses a decoy to lure the thieves out of hiding, but they adduct Doris.