Consider Stevenson's other works, including Treasure Island and the incomplete but legendary Weir of Hermiston.
Consider Stevenson's predecessors in Gothic literature and/or horror, such as The Mysteries of Udolpho by Anne Radcliffe and Frankenstein by Mary Shelley, or those that came after him, such as Dracula by Bram Stoker.
Consider books inspired by Dr Jekyll and Mr Hyde, such as Valerie Martin's Mary Reilly.