An interesting piece of trivia is that the book that we have is Stevenson’s second attempt at the novel. After he wrote the first version, based on a dream, his wife burnt it after judging it to be “utter nonsense.” He then had to rewrite it from scratch.
That was what I thought, too. But there’s a letter written by his wife where she says that she is going to burn it, so that seems to be the accepted version. Either way, it’s a great story.