A young cinema employee becomes entangled with a dangerous criminal organization, setting off a lethal chain of events that Inspector French must unravel. After the woman seeks assistance from a solicitor and subsequently approaches Scotland Yard regarding the mysterious 'Purple Sickle,' her sudden death in Southampton Water forces French to investigate a series of connected homicides. The narrative follows the methodical police work of the inspector as he navigates the deceptive layers of the criminal trio's operations. The story unfolds through a traditional investigative framework, emphasizing the logical progression of evidence gathering and the systematic dismantling of a criminal conspiracy.

This work is characteristic of the Golden Age of detective fiction, emphasizing the procedural rigor and logical puzzle-solving that defined the genre during the mid-twentieth century. The narrative structure relies heavily on the steady, unflappable nature of Inspector French, whose methodical approach provides a stable anchor for the unfolding criminal plot. Readers familiar with the era's conventions will likely recognize the focus on forensic detail and the step-by-step reconstruction of events that lead to the final resolution. The book serves as a representative example of the author's commitment to the 'police procedural' style, prioritizing the mechanics of investigation over psychological introspection.