alt Hacker News> There doesn't seem to be a lot of fiction that features the Pinkertons prominently. One exception is the (excellent) HBO TV series Deadwood.
Also any of Dashiell Hammett's Continental Op stories. The Contintental Detective Agency is the Pinkertons with the serial numbers filed off. Hammett himself worked as a Pinkerton, among other things, before he got into writing.
I got into his writing because Raymond Chandler was such a big fan as I learned from his essay The Simple Art of Murder[1]