The Spy of the Rebellion, Being a True History of the Spy System of the US Army During the Late Rebellion

"Revealing many secrets of the war hitherto not made public. Compiled from official reportsprepared for President Lincoln, General McClellan and the Provost-Marshal-General. " The author, Allan Pinkerton, under the name of Major E. J. Allen was chief of the US Secret Service. Originally published in 1883.