This was a rather tortured fantasy and mystery story combined. I needed to read it twice all the way through to fully grasp it. Written in 1894 it is contemporaneous with Arthur Conan Doyle's mysteries starring Holmes and Watson. It is fun to note the similarities and differences between the two takes of the same genre. By the end of a Sherlock Holmes story, every detail makes perfect sense. A crime was committed. Holmes finds out about it, deduces the facts of the case in a remarkable manner, proceeds to solve, and eventually brings the criminal to justice, setting the formula for the sleuth solved mystery in granite. Ready for the next case.
Machen didn't get the memo, and his concept is therefore quite different. Machen sets his mystery in the same London of the same period and has a sleuth solve a crime. Machen's sleuth, named Doyle ironically enough, likewise is super-powered, it seems, in deductive reasoning. There the similarities end. Unlike with Holmes' methods, the reader is never let in to see how Doyle makes his deductions, only that he does. This is really odd, like a key part of the story is being omitted.
Doyle does have a partner named Salisbury, but Salisbury is no Watson. Salisbury has no intention of chronicling Doyle's exploits. To the extent Salisbury helps Doyle it's accidentally on purpose. Really. Read the story if you don't believe that can be done. In fact, Salisbury is so the opposite of Watson that once he has finished the mission he is assigned in Machen's novel as Doyle's facilitator, he wants nothing further to do with Doyle, or the case. He certainly has no interest in how it turns out.
So how then is Machen to get the details to us readers if there is no Watson to chronicle it? That's the tortured part. Machen has to finally resort to a letter written by another character altogether to convey the solution of the crime to the reader.
Flawed as the story may be, there are a lot of fun elements to it. Machen gives us unabashedly mystical elements with a scientific explanation half-attempted of human brains being changed into devils' brains, which makes the homocide justified. What remains after that is less a real mystery than a drama, all of which takes place oddly off-screen. The authorial technique really makes this into a hot mess of a story, with not everything explained.
There is no way an Arthur Conan Doyle reader would have tolerated the kinds of ambiguity this weird story ends on. To an extent, I don't either. However, despite its technical flaws, there is something really appealing about this messy story. The atypical characters are a joy. I love the fantastic events that take place in such a humdrum urban setting. The story's lack of plot polish even works for me. I admire Machen for aiming high, for what he tried (but I think ultimately failed) to pull off. At least it's truly unique and interesting.
There is one thing I wish I had known coming in to this story that might have saved me the trouble of reading it again in order to figure it out, and that is who is telling the story. If you want, I will share my deductions with you. Maybe it will help. The story is divided into five unequal parts told in different ways.
I. Dialogue between Doyle and Salisbury, primarily Doyle telling first half of Dr. Black's story.
II. Third person omnicient focused on Salisbury.
III. Third person omnicient focused on Salisbury. Transition into dialogue between Doyle and Salisbury with Doyle telling the second half of Black's story.
IV. Third person omnicient focused on Doyle.
V. Letter from Dr. Black explaining many plot elements while leaving others still unclear, such as how the jewel was acquired in the first place.
Another reviewer stated Machen wrote other stories featuring mystic sleuth and successful author Doyle solving supernatural crimes. Searching through my Machen collection, I found more than six but less than a dozen such stories, all novelette length or shorter. I'm hooked and plan to read them all eventually. They have to get better as Machen gains experience writing them. I'll update this review with the stories' titles when I do.