The rigid police protection which had at first been imposed upon both the Professor and Mr. Ludgrove had been gradually relaxed until now it had dwindled to nothing more serious than a casual glance at their houses by the constable on beat when he happened to pass them. The professor himself appeared to have forgotten the warning given to him by the Black Sailor, and to have acquiesced in the official view that, since the perpetrator had committed suicide, nothing further would be heard of the murders.

It was while matters were in this state that Dr. Priestley received one Saturday morning a letter which obviously caused him some satisfaction. It was signed “Elmer Ludgrove” and was written in a curiously neat and clerkly hand. The contents of it were as follows: