The intended wedding of Captain Hugh “Bulldog” Drummond (John Howard) to Phyllis Clavering (Louise Campbell) at her villa in Switzerland is stopped short (once again) when someone murders the Swiss policeman who is guarding their wedding presents. The killer makes off with their prize possession, a synthetic diamond, made by a secret process by Professor Bernard Goodman (Halliwell Hobbes), the father of their good friend Gwen Longworth (Nydia Westman).

