A scholarly book that, from its title, sounds fascinating--and actually is. Mom's time flame is the 1855-1930 period, when the agency founded in Chicago by Scots immigrant Allan Pinkerton (Chartist, abolitionist, then robber-baron ally) served as a ""weathervane in the social history of the United States."" The rise of detective agencies in the 1850s followed the railroads' growth, as a response to regional crime in the absence of regional police. Pinkerton occupied the field early, specializing in ""testing"" programs (i.e., spying on employees). By 1860, the agency amounted to a regional midwestern police force; and though Allan Pinkerton's brief Civil War service was lackluster (his Confederate troop over-estimates ""contributed significantly to McClellan's inherent 'slows,' "" says Mom), it boosted his administrative experience and let him go national. Postwar, the agency remained tied to the railroad and express industries, while Pinkerton himself took to writing fictionalized case-histories (e.g., ""The Gypsies and the Detective"") and ""serious"" books on crime. The point was image: Pinkerton wanted to professionalize both the industry and the occupation, and to set himself up (like J. Edgar Hoover later) as a public educator. Mom's tracing of the agency's ups-and-downs and shifts in operational emphasis in the 1880-1910 period under second-generation Pinkertons--Robert (serious, businesslike, and patrol-guard-oriented) and William (sometime-drunk, pal of hightone crooks, and detective-oriented)--is first-rate social history. As railroads' reliance on outside agencies for crime-solving decreased, Pinkerton's turned to union infiltration and ""strike service"" (providing guards and scabs)--winning a well-earned anti-union reputation, capped by the famous 1892 Homestead strike violence. (""Father was killed by the Pinkerton men,"" ran a popular tune.) Amid public disapproval and a congressional inquiry, Pinkerton's shifted back to detective work, lining up lucrative bank industry protection contracts in the era when hobo-burglars (""yeggmen"") roamed mid-America. Here, as Morn points out, the success of Pinkerton's and its competitors forded the public police to gear up for national cooperation. And as urban and State police improved and the FBI established itself, Pinkerton's moved back into guard and protection service, where it remains. Throughout, Morn highlights recurrent themes: private detectives filling a gap created by inadequate public policing; the protection/detection pendulum; and the private eye's quest for respectability in a society whose professed ideals of honesty and openness seemed, by definition, at odds with the nature of his work. An excellent study that deserves more than an academic audience.