“That was only a recovery, not a gain,” I said.

“No,” he replied, “it garnered something when it fell. To misquote—as both of us like doing—‘Cast your pen upon the waters and in a few moments it may pick up more copy than if you’d written for a week with it!’”

My “What do you mean?” was checked as he carefully unscrewed the top.

“See those little holes,” he said, pointing to small openings just under the shoulder of the nib; then he drew out the small inner tube. It wasn’t of rubber—it was of glass and was full of fairly clear water.

“This is water—water from the pond in the bird sanctuary. It looks like ordinary pond-water. As a matter of fact, it contains an unusually interesting form of life in it.”

I began to feel a faint uneasiness.

“Oh, don’t be alarmed. It is safely under screw and stopper now and is only being kept as Exhibit A—or, if you like it better, a stage-property in a forthcoming dramatic performance which will be Act Three of the mystery play in which you starred in Act Two, Scene Two.”

“But I don’t quite see . . .” was met by Mr. Mycroft more graciously than usual with, “There’s really no reason why you should. I couldn’t quite see myself, at the beginning. Yes, I do indeed admire such richness of double-dyed thoroughness when I come across it. It is rare for murderers to give one such entertainment, so elaborate and meticulous. They usually shoot off their arrows almost as soon as it enters their heads that they can bring down their bird and without a thought of how it may strike a more meditative mind afterward. But this man provided himself with a second string of rather better weave than his first.”

Well, when Mr. Mycroft gets into that kind of strain it is no use saying anything. So I swallowed the I.D.S. formula that was again rising in my throat and waited.

“You remember, when you helped me to my feet and the pen had been salvaged, that with your aid we completed the round of the little lake. But when we had gone no farther than the beginning of the high-backed bridge, I felt I must rest. Do you recall what I did then?”

Could I recall! Naturally, for that was the very incident that had confirmed my suspicion that Mr. Mycroft was really shaken. I answered brightly:

“You sat, I can see it now, and for a moment you appeared to be dazed. And while you rested, as the beautiful old song, “The Lost Chord,” expresses it, your ‘fingers idly wandered.’ But I noticed that they must be getting dirty, because, whether you knew it or not, they were feeling along under the jutting edge of the slab that made the step against which your back was resting.”