Originally Posted by lila55
I nominate "The Woman in White" by Wilkie Collins. Available for free in these places
"Secrets, mistaken identities, surprise revelations, amnesia, locked rooms and locked asylums, and an unorthodox villain made this mystery thriller an instant success when it first appeared in 1860, and it has continued to enthrall readers ever since. From the heroís foreboding before his arrival at Limmeridge House to the nefarious plot concerning the beautiful Laura, the breathtaking tension of Collinsís narrative created a new literary genre of suspense fiction, which profoundly shaped the course of English popular writing." (Amazon
I'll second this. Been wanting to read Wilkie Collins for a while.