Crook Dominic Colpoys-Owen (Terence Morgan) has his eye on the loot inside an embassy in London, when foreign ambassador's daughter Seraphina (Yoko Tani) unwittingly reveals her father, away on business, has left big money behind in the safe. Colpoys-Owen works his smooth-talking charm on the innocent girl, who becomes so infatuated that she agrees to help his gang with its plan. This involves a robbery accessed from the London Underground on the embassy in Knightsbridge.