"The Door of the Unreal" (1920) is an early werewolf novel by Gerald Biss. From the Foreword:
"As to my subject, which policy forbids me even to hint at in my foreword, I can only say that it is one common to the folk-lore of all Eastern and European countries, and found in the annals of America itself, if to a lesser degree. That of itself forbids light dismissal of the matter as beyond the bounds of credulity, and in the Near East it was accepted as a fact, at any rate, up to 1914, and since then the horrors of war and the worse horrors of Bolshevism have taught us that nothing is too ghoulish to be true. I can only add that I have read and searched many authorities in writing this book, and have not embroidered or exaggerated accepted facts for any purpose of sensationalism. Legends so world-wide and so generally accepted give pause. I myself unexpectedly learnt a great deal in the writing of this book and in my drivings into the lore of the uncanny."