Unflinching — Stuart G. Yates

In the brutal, unforgiving West a dozen years after the California Gold Rush, a lone Pinkerton detective is on the trail of two vicious killers.
When a famous ex-general's daughter is kidnapped, Detective Simms is assigned with bringing her home. Forged in the Mexican War, this man of steel knows how to survive and how to kill. But he will need all of his skill and guile if he is to survive this unforgiving land, and bring the general's daughter home.
And then, it gets personal...