The Woman in White by Wilkie Collins
Walter Hartright, is walking down the street, his mind absorbed with his own problems, when suddenly a woman, dressed in white appears. She is clearly scared, and he walks with her toward London, eventually putting her in a cab and seeing her off. Shortly thereafter he is informed by two men who are chasing her that she had escaped from an asylum. And that's all we see of the lady in white for now.
Hartright is left with a mystery. He takes a job as a drawing master, instructing two half-sisters as different as night and day. One is fair, and one is dark. One is pretty, and one is…well…unattractive. Marian is brave, brilliant, and resourceful, a marvelous character given the time period. Marian can hold her own. Hartright, of course, falls in love with Laura Fairlie, the fair and beautiful one, an heiress, an orphan, a woman in need of protection. Unfortunately, she is engaged to Sir Percival Glyde....