Bill James 
In the Absence of Iles [EPUB ebook] 

Assistant Chief Constable Desmond Iles misses a crucial conference and is not able to give vital advice to a colleague, Assistant Chief Constable Esther Davidson. She is having big trouble from a local gang known as the Guild, and proposes to put an undercover spy into the criminal outfit. Iles might have been able to dissuade her from such a rash move. One of his own undercover officers was murdered not long ago. But Esther goes ahead, with terrible consequences . . . 'James continues to produce the most realistic, unsettling sequence of novels, recording the subtle relationships between police and villains’ The Times