"The history of Civil War espionage is usually mentioned only in passing in general accounts of the war. Lying under a cloud of romanticism, its details have had to be ferreted out in specialized sources. For his complete account of the subject, Markle draws upon just about all the available material and summarizes it with judgment, balance, clarity, and occasional wit. Among the subtopics are technology (photography for mapmaking and Confederate use of a forerunner of microfilm), the value of women spies (less subject to suspicion, they could move with greater freedom than male spies), and the roles of blacks as spies. A good case could be made that this volume is the single most valuable contribution to general Civil War literature so far this year. "—Booklist