“I’m in a business where people come to me with troubles. Big troubles, little troubles, but always troubles they don’t want to take to the cops.” That’s Raymond Chandler’s Philip Marlowe, succinctly setting out our image of the private eye. A no-nonsense loner, working on the margins of society, working in the darkness to shine a little light.

The reality is a little different—but no less fascinating. In The Legendary Detective, John Walton offers a sweeping history of the American private detective in reality and myth, from the earliest agencies to the hard-boiled heights of the 1930s and ’40s. Drawing on previously untapped archival accounts of actual detective work, Walton traces both the growth of major private detective agencies like Pinkerton, which became powerful bulwarks against social and labor unrest, and the motley, unglamorous work of small-time operatives. He then goes on to show us how writers like Dashiell Hammett and editors of sensational pulp magazines likeBlack Mask embellished on actual experiences and fashioned an image of the PI as a compelling, even admirable, necessary evil, doing society’s dirty work while adhering to a self-imposed moral code. Scandals, public investigations, and regulations brought the boom years of private agencies to an end in the late 1930s, Walton explains, in the process fully cementing the shift from reality to fantasy.

Today, as the private detective has long since given way to security services and armed guards, the myth of the lone PI remains as potent as ever. No fan of crime fiction or American history will want to missThe Legendary Detective.