Spies On Neither Side
Quinn Matheson isn't a spy. But that won't matter to the military—Union or Confederate—if they discover that she's gathering intelligence for a group of businessmen who have money invested in Mexican enterprises. And that won't be all they'll find. Quinn has been masquerading as a young boy for the duration of the war.
When war came, circumstances put Quinn and her family on opposite sides of the battle fronts. In need of a means of supporting herself, she dresses as a boy and takes a job with the short lived Pony Express. Her last job is to carry word of the war to the border when she's recruited to work for the British businessmen.
The dangerous demands of Quinn's job become routine as the war the was supposed to burn itself out quickly doesn't. But everything is turned upside down once again when Quinn's mentor dies and his replacement arrives. Nathan Reese doesn't seem to notice that his best operative isn't a half breed boy. He's too intent on finding the girl he has been searching for since before the war.
When Quinn and Reese are exposed, they manage to escape back into the world they knew before the war, only to find that their troubles are far from over.