Nickson, Chris. Cathy Marsden thriller

"Leeds, 1941. As the war rages across Europe, Police Sergeant Cathy Marsden's life since she was seconded to the Special Investigation Branch has remained focused on deserters and home-front crimes. Until now. Things take a chilling turn when Cathy's civil servant brother, Dan, arrives from London with a dark secret: he is working for the XX Committee - a special MI5 unit set up to turn German spies into double agents. But one of these agents has escaped and is heading for Leeds, sent to destroy targets key to the war effort. Suddenly Cathy and the squad are plunged into an unfamiliar world of espionage and subterfuge. With the fate of the country and the war in the balance, failure is not an option, and Cathy must risk everything, including her own life, to stop a spy." --