Maria Isabella Boyd's success as a Confederate spy has made her too famous for further espionage work, and now her employment options are slim. Exiled, widowed, and on the brink of poverty, she reluctantly goes to work for the Pinkerton National Detective Agency in Chicago.

Adding insult to injury, her first big assignment is commissioned by the Union Army. In short, a federally sponsored transport dirigible is being violently pursued across the Rockies, and Uncle Sam isn't pleased. The Clementine is carrying a top secret load of military essentials - essentials that must be delivered to Louisville, Kentucky, without delay.

Intelligence suggests that the unrelenting pursuer is a runaway slave who's been wanted by authorities on both sides of the Mason-Dixon for 15 years. In that time, Captain Croggon Beauregard Hainey has felonied his way back and forth across the continent, leaving a trail of broken banks, stolen war machines, and illegally distributed weaponry from sea to shining sea. And now it's Maria's job to go get him. He's dangerous quarry, and she's a dangerous woman, but when forces conspire against them both, they take a chance and form an alliance. She joins his crew, and he uses her connections. She follows his orders. He takes her advice. And somebody, somewhere, is going to rue the day he crossed either one of them.