In a way, I wish I'd had no idea this book was about [STOP READING NOW IF YOU DON'T WANNA KNOW WHAT THIS BOOK IS ABOUT!:] a man who turns into a werewolf. Or rather, I wish it was possible to read this book in the time it was written. I only say that because, knowing the "mystery" going into it, the first half of the book I found myself just waiting for the main character to catch up to where I was, then let the other protagonists know, and on and on.
The story seems somewhat basic for a werewolf story: couple missing people, one found looking savagely attacked by an animal, a strange new tenant in a house in the woods, one man and his intelligent friends suspecting something out of the ordinary going, the revelation of lycanthropy, etc, etc.
I guess that is basically as basic as a werewolf story can get, but then I keep in mind that this was written in 1920 and probably seemed a hell of a lot more original at that time. So, certainly no strikes against the book for the story itself, which is a good, if not outstanding, tale.
The writing itself is very absorbing, and the book moves along at a fluent, relatively fast pace. The creepy characters are very creepy, and the noble good guys are very noble, and everyone seems to follow in a "Dracula" style tradition. I noticed a few similarities to that book, which would have been written about 25 years before "The Door of the Unreal." That's not a bad thing, though, as "Dracula" pretty much set the standard for horror stories about creepy guys living in secluded houses, being hunted by a group of kind-hearted monster killers.