Hardcastle's Mandarin by Graham Ison

Detective Inspector Ernest Hardcastle of Cannon Row Police Station is one of the old fashioned stand-no-nonsense coppers who kept the streets safe in the early years of the twentieth century. In this his seventh case accompanied as always by Sergeant Marriott he investigates the murder of Sir Nigel Strang, Permanent Secretary at the Ministry of Munitions and as senior civil servants are popularly known as "Mandarins" the title of the book is explained. Scotland Yard's Special Branch become involved, much to his annoyance, as German Intelligence are suspected of the crime. Hardcastle, however, prefers to stick to tried and trusted police methods and discovers that Sir Nigel's private life is not that of an upright pillar of the establishment that his widow would have them believe. Another murder is committed and this time German spies may well be involved but so is a low level criminal well known to the police. Inspector Hardcastle, politely but firmly, ploughs his way through all ranks of society until he brings his man to justice at the end of another satisfying story. I look forward to more of his investigations.