Riuscirà il nostro eroe a ritrovare il più grande diamante del mondo?

Jimmy Logan, a detective, tries to retrieve a diamond of the British crown, stealed by the infidel chief of the English Secret Service. After carrying out dangerous investigations at Montecarlo, Beirut and Hamburg, he lately discovers that the head quarter of the thieves is a mental hospital. Unfortunatelly the fabulous diamond ends his run under a roadroller.