The film stars Hugh Sinclair as Simon Templar, also known as "The Saint", a world-roving crimefighter who walks the fine edge of the law.

It was Sinclair's first appearance as Templar, having taken over the role from George Sanders, who then stepped into RKO's "Falcon" series.

Most of the story takes place in Switzerland, where Templar interrupts his holiday to retrieve a missing secret code.

The key to the mystery is a Swiss music box with a most unusual tune, diligently sought after by enemy agent Rudolph and British secret service operative Valerie.

Templar is aided in his investigation by reporter Mary Langdon and Monty Hayward, with Inspector Teal of Scotland Yard.