Michael Gilbert 
Roller-Coaster [PDF ebook] 

Patrick Petrella has been promoted, but is now installed behind a desk, dealing with a mountain of paperwork on diverse subjects ranging from police race relations to allegations of brutality, press harassment and bribery of officers. He is, however, desperate to get out onto the streets again. In a fast moving novel Gilbert has Petrella detecting the patterns of rival gangs at work and uncovering a paedophile ring which operates as far as Amsterdam. He is soon taking on one of the more unsavoury and unscrupulous outfits in London and a surprising outcome enables him to map out the direction to take. There is violence, dark-humour and fast action in this gripping story.