A tracing of crime from Quantrill's during the Civil War to the Kansas City Massacre. It's not an overview of the era -- he traces some connections, rather -- though he does diverge quite a bit to explain circumstances.
Train robberies, bank robberies, cold-blooded murders, daring rescues, daring captures -- and not so daring captures. Some of it is speculative, such as why the James gang gratuitously murdered a young man in their first bank robbery, and which one did it. Motives, such as a number of crimes that seemed to be done out of flamboyant desire for fame. And the changes as the west was tamed.
A lot of interesting stuff. Not particularly gory in retelling, though there are a lot of deaths.
Indeed, this was first published in 1960 -- and the author can talk of his having talked with some of the participants.