Simon and Schuster
Douglas Waller, a former journalist who has written several books on twentieth-century American intelligence operations, here provides a lively and informative treatment of many episodes of Civil War espionage and counter-intelligence, focusing on four Union agents and officials: Allan Pinkerton, Lafayette Baker, George Sharpe, and Elizabeth Van Lew, all active almost exclusively in Washington, Richmond, and the Eastern Theater.
Johnson, Martin P.
"Lincoln’s Spies: Their Secret War to Save a Nation,"
Civil War Book Review: Vol. 21
Available at: https://repository.lsu.edu/cwbr/vol21/iss4/10