I have always had a lot of fun writing mystery plays, although a well-built mystery drama represents a staggering amount of hard work. The formula is a very exact and very exacting one, and in addition to its mechanical difficulties the author must not only create an interest in who committed the crime, but, if he hopes for success, he must make them fear that some one character dear to them is guilty. In other words, the mystery play in which one hasn’t gone deep enough into the emotions to make the audience care who committed the murder is never successful, no matter how mysterious it may be. Emile Gaboriau was the master of this form of writing, and to this day we all more or less faithfully follow his model, although his complicated plot structure requires more skill and patience than most modern authors are able to supply. Poe borrowed the formula, as he quite frankly admitted, and from him it descended to Anna Catherine Green, whose LEAVENWORTH CASE and HAND AND RING are fine examples of this form of writing. Jumping again across the Atlantic, we see in the Sherlock Holmes character, and in Watson’s shrewd “feeding” of that character strong traces of the Gaboriau style. After these came the deluge: Bayard Veiller, with his almost perfect THE 13TH CHAIR, several of my own and many others leading up to the endless stream of mysterious murders, strange disappearances, midnight crimes, haunted houses, etc., etc., etc. I know hundreds of men who read one at one sitting, but I defy any man to write one in less than one hundred hours of solid work. When I tackle a job of this sort, my study looks like an architect’s work room, charts everywhere, on the wall and tables and even on the floor. I make a chart for each character, showing exactly where he is, what he says and what he is thinking of each moment of the play. In this sort of trick writing, every word one says is extremely likely to be used against him. Next to rough farce, the writing of a play of this sort calls for more technical skill and inventive power than any other form of play making.