An Agent for Lucy by Amelia C. Adams

Lucy Haskell is returning home to Denver after four years of living abroad in China. She’s eager to see everything that has changed in her absence and to start the next chapter of her life. When her dear friend and traveling companion Delphine Collins goes missing without a trace in Chinatown, Lucy realizes she’s in a unique position to help, and she decides to apply to become a Pinkerton agent.
Jed Green isn’t sure what he thinks about ladies joining the agency. He knows from personal experience that it’s dangerous work, and he can’t imagine putting a woman in those kinds of situations. When he’s asked to train a new female agent, he agrees reluctantly, but when he’s asked to marry her for propriety’s sake? That’s another thing altogether – a preposterous thing.

Before Jed and Lucy can concentrate on their case, they must discover if they can work together. Then they must resolve their new feelings so they can work on the case.