The Gray Chamber by Grace Hitchcock

Edyth Foster is a talented, eccentric heiress, who doesn't give a whit what society thinks! She fences, rides her velocipede, and doesn't wear a corset or often even a hat. Her fencing instructor Bane knows she is a world class opponent, but hasn't thought of her in any other way for years since he started teaching her as a young girl. So far, it has escaped him that she is now a woman of five and twenty and drop dead gorgeous as well! When he does realize that fact, What follows is not what you might expect...including treachery, revealed past secrets, a Pinkerton agent and Nellie Bly! I won't spoil the story, but it is a wonderful read!