Allan Pinkerton was the founder of Pinkerton's National Detective Agency. In early 1861, while employed by the Philadelphia, Wilmington & Baltimore Railroad, Pinkerton discovered and thwarted a plot (the "Baltimore Plot") to assassinate President-elect Lincoln. Working for General McClellan, Pinkerton organized a secret service for the Department of the Ohio and the Army of Potomac. Pinkerton's successes came primarily in the counterintelligence field, and his exploits in the realm of positive military intelligence collection are not highly regarded. Pinkerton's work in military intelligence ended with McClellan's dismissal following the Battle of Antietam in November 1862.
In detailing the various events Pinkerton was careful to offer nothing but that which actually transpired. He has avoided giving expression to any thoughts or feelings of antagonism to the South, because the time for such utterances has passed.
Mr. Pinkerton's memoris go far beyond merely conveying historical information, narrowly understood. The Spy of the Rebellion also serves historical comprehension in the same manner that good fiction often does, though almost subconscious means, thorough an indefinable "feel" for the milieu that it imparts to the reader.