When the quiet, unassuming, newly-promoted Chief Inspector French is directed to investigate the seemingly impossible safebreaking at a London diamond merchants, he quickly realises the precarious nature of the company's finances is unlikely to be coincidence, and that there may be more than meets the eye to the recent death of the company accountant.
The Inspector French novels are early examples of the police procedural genre of detective novels, and their description of detailed, methodical police work, carred out by modest and dogged officers, is in marked contrast to the flights of inspired genius or devil-may-care derring-do of the majority of crime novels of the period (written in 1935).
The plotline is a little slow to develop, as FWC lays the groundwork of describing the predicament of the failing diamond merchant and its board of directors, and the weekend party at a Guildford country house held to hammer out their way forward, but, once French enters the narrative, the reader is inexorably drawn into the Chief Inspector's investigation and his careful consideration of all that he finds. The detective ultimately relies on a some lucky breaks as well as his logical, painstaking procedure, but that is often the case in real life, too, and falls comfortably within the realm of plausibility.
A good read, and one which, despite reliance on some of the tropes of the time (class distinction and deference, country house setting, and mannered behaviour), helps lay the foundations of the modern police procedural. I would give it a 6.5 out of 10.