One particularly famous incident (after the founder's death) was the Homestead strike [1]. Strike-breaking was very much in the Pinkerton's wheelhouse and it's a good example of what they were actually used for [2].
There doesn't seem to be a lot of fiction that features the Pinkertons prominently. One exception is the (excellent) HBO TV series Deadwood.
It's particularly apropos at this time because the lawless violence and organized labor suppression of the robber barons in the Pinkerton era is very much the future we are careening towards.
[1]: https://www.pbs.org/wgbh/americanexperience/features/carnegi...
[2]: https://allthatsinteresting.com/pinkerton-detective-agency
There's also The Tall Target, a 1951 movie that sometimes gets played on classic movie channels, which is about the "Baltimore Plot" in which Abraham Lincoln was supposedly going to be assassinated on his way to his first inauguration in 1861. Supposedly it was prevented by the Pinkertons, although historians question if any real plot was planned.
https://en.wikipedia.org/wiki/Baltimore_Plot https://en.wikipedia.org/wiki/The_Tall_Target
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]
https://reddead.fandom.com/wiki/Pinkerton_National_Detective...
Deadwood was particularly good because it not only featured Pinkertons but painted them really well as the defenders of the wealthy and basically just a large and well-funded gang.
But worst game? Surely it's better than something like Manhunt 2?
There's a long Clive Cussler series about the "Van Dorn Detective Agency", which is clearly the Pinkertons.[1] Willie Sutton, the bank robber, wrote of the Pinkertons, "They were as powerful as the cops, and much better organized."
Pinkerton, the company, is still around, but they haven't done much detective work since the 1960s. Now they're mostly a security guard service.
For all the faults the FBI has I don't think Pinkerton's paid by Musk are a good alternative.
The Pinkertons were breaking strikes launched by Americans, after all. May Day is a commemoration of an event that took place in Chicago. The reaction to the cold-blooded murder of an insurance executive on a public street is pretty characteristically American, in my view. We just don't like power.