The Vanishing of Lord Vale by Chasity Bowlin

Elizabeth Masters has put her scandalous and painful past behind her. She's taken a position as companion to the tragic Lady Vale and her primary duty is to dissuade the woman from believing that everyone from the butcher's delivery boy to the ostler at an inn is her missing son. But a late-night visit to an alleged mystic in the city of Bath results in near-tragedy as Elizabeth is nearly abducted by ruffians waiting for them outside. They are rescued by a handsome and mysterious stranger who calls himself Benedict, the very name of Lady Vale's lost son. 

Benedict has his own reasons for being in Bath - to locate his missing sister and see her safe once more. Waylaid by a pistol ball from the men who attacked Miss Masters, he finds himself dependent upon the assistance of Lady Vale to rescue his Mary. In exchange, he must consent to her investigation of his past to determine if he is, in fact, her missing son, an unlikely scenario in his mind. 

Forced to work together, Benedict and Elizabeth cannot fight the attraction they feel for one another. Yet with every piece of evidence uncovered, the truth of Benedict's identity threatens their burgeoning relationship...and the danger that brought them together looms larger at every turn.