Wild Card by Caroline Lee

He’s come home for revenge.
Everything was going fine in Jack’s life…until she showed up. He was living the high life in a European court, friend to princes and courtesans alike, learning witty repertoire and interesting new ways to kill enemies, and then this cute little package claiming to be a Pinkerton agent—a Pinkerton, imagine!—lands in his lap. That wouldn’t have been so bad—she’s really quite delectable—except she’s bringing a message from his mother, and now duty demands Jack Hoyle return to the home he hasn’t thought of in years.
Tavie Smothers is a master—mistress?—of disguise. The talent has served her well during her years with the Pinkertons, but this case is officially her last. Mr. Augustus King is holding the entire town of Black Aces, Montana, hostage; bleeding the businessowners and families dry in his effort to fool potential investors into thinking his silver mine is still salable. Everything he’s doing is legal…but Tavie can’t stand by and let him win.

So she brings in a wild card.
Mr. King might understand poker, but he’s never encountered an opponent like Jack. Because Jack, despite his unorthodox methods and his cold refinement, is determined to avenge his father’s death and protect the town’s legacy. Add in an equally resolute ex-Pinkerton in disguise, and they’re betting on a sure thing.
But there are no sure things in love and poker, and Mr. King still has an ace up his sleeve…