FIRST RULE: Don't lose your concentration.

Electra McDonnell and her family earn their living outside the law. Breaking into the homes of the rich and picking the locks on their safes may not be condoned by British law enforcement, but with World War II in full swing, Uncle Mick's locksmith business just can't pay the bills anymore.

SECOND RULE: Don't make mistakes.

So when Uncle Mick receives a tip about a safe full of jewels in an empty house, he and Ellie can't resist. All is going as planned-until the pair is caught red-handed. But instead of arresting them, government official 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.

THIRD RULE: Don't get caught.

Ellie doesn't care for the major's imperious manner, but she has no choice. However, when they break into the house, they find the safe open and empty, and a German spy dead on the floor. Soon, Ellie and Major Ramsey are forced to put aside their differences to unmask the double agent, and stop Allied plans from falling into enemy hands.