Pre-war intelligence man Tommy Blythe interrupts his honeymoon to investigate the discovery of vital Air Ministry blueprints on a woman killed in a London road accident. The trail leads to a boarding house in Notting Hill and its varied tenants.

Undercover agent Robert Leyland entraps crooks trying to sneak expensive goods past customs on transatlantic crossings. After Leyland falls for reluctant smuggler Barbara Standish, he convinces her to return with him to France with her cache of diamonds. But she is unaware of a network of thieves onboard their ship, competing against each other to make off with her jewels.

A complicated adventure involving twin brothers and the Foreign Office trying to thwart the ambitions of a hostile sheikh.