A husband-and-wife detective team look into the murder of one of her friends, whose father--a prominent scientist--has been kidnapped. They find themselves up against a sinister crime organization headed by a mysterious figure known only as "Z".
When she learns that the Nazis have confiscated Leonardo da Vinci's masterpiece Mona Lisa, art-loving South American wanna-be spy Tamara (Jane Carr) journeys to Lisbon to snoop for the Germans in return for the iconic painting. But bumbling Nazi agents, Allied counterspies and multiple copies of the artwork soon confound her attempts at espionage.
Charters and Caldicott are touring the Middle East. After visiting Saudi Arabia they find themselves in Bagdad where they are mistaken by a group of German spies for the messengers who are to carry a song record by beautiful singer La Palermo which contains secret instructions of the German Intelligence. Realizing their error, the German spies follow Charters and Caldicott to Istanbul and Budapest, trying to eliminate them and retrieve the record.
A shy British teacher looks back nostalgically at his long career, taking note of the people who touched his life.
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.