The Judas Sheep — Stuart Pawson

Detective Inspector Charlie Priest is officially on sick leave, but this brief break from work comes to an abrupt end when Mrs Marina Norris's chauffeur is found dead from unnatural causes - namely a blast to the head from a Kalashnikov.
Meanwhile, big-time drug smugglers on the Hull-Rotterdam run demand his attention. His contact, Kevin, is a lowly cog in the great smuggling wheel, and easily hoodwinked into believing that Charlie's line of business is similar to his own. But the real villains are not such pushovers, and when Charlie uncovers a connection with his previous enquiry he realises that he's on very dangerous territory indeed.