In the Blood — Stuart G. Yates

Less than a year after crossing the uncharted Territories of the Old West in pursuit of vicious killers, Detective Simms of the Pinkerton Detective Agency receives orders for another mission.

The fledgling railroads cut through the endless plains, and desperadoes are taking advantage. The Pinkertons are charged with protecting the trains and the money they hold, but someone knows how much this is, and that someone must be stopped.

But as Simms shadows the train robbers, he begins to realize that someone is shadowing him. It is certain that one of them will end up six feet under... by the bullet.