A diamond merchant is found murdered beside an empty safe, and the meticulous Inspector French must track a master criminal across Europe. The investigation into the robbery and murder of Mr. Gething at Duke and Peabody, a Hatton Garden diamond merchant, reveals multiple suspects. Inspector Joseph French of Scotland Yard begins a methodical inquiry, following a trail that leads from London to international locales including Holland, France, and Spain. The case culminates on a ship bound for South America, where the perpetrator's identity and the stolen diamonds are finally confronted.

As the inaugural novel featuring Inspector French, this work establishes the character and the author's reputation for intricate plotting. The narrative's strength lies in its detailed procedural approach, which was highly regarded by contemporary critics and readers of detective fiction. The story's methodical unfolding and international chase elements are key to its appeal. This case is considered a prime example of Freeman Wills Crofts's ability to construct complex mysteries that reward careful attention to detail.