As Britain's economy takes a hard hit in World War II, Ellie McDonnell and her family earn their living by burglarizing the homes of the wealthy. When Electra and her Uncle Mick are caught red-handed, Major Ramsey has an offer: either Ellie agrees to help him break into a safe and retrieve blueprints crucial to the British war effort, or he turns her over to the police. In her debut outing, Ellie agrees, but when she later finds a German spy dead, she and Major Ramsey are forced to put aside their differences to unmask the double agent, and stop Allied plans from falling into enemy hands.