Solemn Graves (A Billy Boyle World War II Mystery) - James R. Benn

July, 1944, a month after D-Day. Billy, Kaz, and Big Mike are assigned to investigate a double murder, close to the front lines in Normandy. An American officer and a member of the French Resistance were found dead in a manor house outside the town of Trevieres. The investigation is shrouded in secrecy, due to the highly confidential nature of the American unit headquartered at the Manoir de Castilly; the 23rd Headquarters Special Troops. This unit had a unique mission within the US Army: to impersonate other US Army units in order to deceive the enemy into thinking they were facing larger forces.