At the offices of Duke and Peabody in London's Hatton Gardens, the body of old Mr Gething is discovered along with an open safe. The diamonds that he had locked away, however, are gone. It is a perplexing case, and obviously one for Inspector Joseph French of Scotland Yard. As the meticulous Inspector puts his full powers behind the investigation, he crisscrosses the continent from London to many locales of Europe. In pursuit of an unknown criminal, will French be able to deduce just who has the diamonds?