The Abandoned Daughter by Bancroft, Blair

Isabelle Bainbridge—abandoned by her gamester father, leery of the young lord who claims he is rescuing her—is more than a little surprised to find herself employed as companion to his grandmother in Bath, who treats her more like a ward than an employee. A near idyllic situation, until Isabelle discovers a young woman’s body floating in the Kennet & Avon canal—an alleged suicide—soon followed by a series of murders that shake the tranquility of the beautiful city known as a refuge for the elderly and infirm.
Although Isabelle is determined to despise her rescuer—the viscount who won her home in a game of cards—she is forced to rely on him as she is stalked and it becomes apparent she may be next on the killer’s list. There are several surprises, as well as moments of terror, before this Gothic adventure finds its happy ending.