Serapion

"I won't any more," broke in Berquist hastily. "But you know that there are entities and forces dangerous to the human race outside of what we call the natural world, and that your investigations are no better than a sawing at the bars of a cage full of tigers. If I thought you could loose them, I have already told what I would do!" Stevens' 1920 novel of demonic possession, unique for its ambiguous ending. First published in Argosy All-Story magazine.