Stuart G. Yates 
Blood Rise [EPUB ebook] 

After the murder of a U.S. Senator, Pinkerton Detective Simms is tasked with bringing the killer to justice.
This would be a simple case for someone as determined and experienced as Simms, but shadowing him is someone far more dangerous and deadly than mere hired murderers.
Across the unforgiving Territories comes a spectre of death, and once again Simms finds himself in a struggle for survival against an old enemy who will stop at nothing to achieve his goal: the death of Detective Simms.
Blood Rise is a standalone novel and can be enjoyed even if you haven’t read other books in the series.