Blood Alone: A Billy Boyle World War II Mystery

Billy Boyle has been landed in Sicily in advance of the main Allied invasion forces. But when he awakens in a field hospital after suffering a concussion, he has amnesia. He doesn't know who he is or where he is, much less what his mission is. His only clue is that he possesses a yellow silk handkerchief embroidered with the initial L and a lot of people seem to be eager to get their hands on this talisman.
As Billy gradually recovers his memory, he recalls that he is his "Uncle" Ike's personal investigator in the European Theatre of War. He had just been promoted to detective in the Boston PD (with a little help from his family and friends) when war was declared. A cushy job on the staff of a distant relative had been his mother's idea, but the relative turned out to be General Dwight D. Eisenhower who decided to put Billy's detective skills to use. Billy discovered, to his own surprise, that he was actually pretty good at his job. Before Billy can remember the dangerous task that has been entrusted to him and do his best to carry it out, several people are murdered. Those opposing him include members of various factions of the American Mafia, as well as soldiers of the German and Italian Armies.
Billy finally remembers his name, but to truly resolve the question of his identity he must dig deep into his soul to discover what kind of man he is.