Western, NY cop goes to CO.

I cant remember the title of this book and its driving me nuts. I read it in 2007,It was a paperback novel. The time setting was was late 1800's,early 1900s?? My memory is kind of fuzzy but I will try to recall it the best I can,It was a western. It starts with a New York police officer who is chasing a mob boss who is dealing drugs and into sex slavery and what not. In the first few chapters the cop ends up chasing him to a train yard where a fight/shootout occurs with the cops partner is either hurt or killed,after that he (the officer) somehow ends up on a train to Colorado,I thought I recalled the town to be Hope ,Colorado but am unsure.Once there he basically becomes the town hero after help ridding the town of opium,child slavery..etc.I cant remember what order the following occured but here are some other tid bits I remember: At one point the officer gets injured and a town doctor hides him in a barn loft and the bad guys find him and he kicks them off the ladder and a brawl breaks out, He saves some Chinese girls locked in a shed who were doped up on opium,The bad guy in town is trying to sell blonde hair blue eyed children to some pirates who I believe was Persian??? Any help with this would be amazing..Thanks

West of the Law by Ralph Compton?

Ordered to head west when a New York gangster puts a price on his head for killing his son, Detective Sergeant John McBride ends up in High Hopes, Colorado -- a lawless boomtown where McBride quickly runs afoul of corrupt saloon owner Gamble Trask and his vicious hired guns. When beautiful card dealer Shannon Roark asks for his protection, it's high time for one of New York's finest to dole out some frontier justice of his own.

wow thank you so very much been trying to remember for some time now and that's it

Found that with a Google Books Search: "new york" "colorado" "opium" subject:"Fiction / Westerns"