The Mistress of Clifftop Manor by Lindsay Hall

It is 1898. Orphaned and penniless, young Lillie Lorimer is thrilled to be hired as governess to the children of railroad tycoon Jay Caldwell. But rather than finding happiness and security in the Caldwell household, she finds herself pitted against forces of terror and doom. Lillie can't escape, for she has fallen in love with the fabulously wealthy, handsome, and charming Jay—a man suspected of having slain his first wife and harboring murderous feelings toward his second, the mentally unbalanced mistress of Clifftop manor.