Certainly it looked very like a case of suicide. But against this theory was the letter found in the dead man’s pocket and the numbered counter. Martin himself might have deposited the latter, as the doctor had suggested, but would he have gone so far as to write a letter which must certainly put the police on the alert when it was found? It seemed highly improbable. Inspector Whyland felt convinced that the death of Mr. Martin was merely another link in the mysterious chain of murders in Praed Street. The evening papers were, of course, full of it, though naturally somewhat guarded. “Another tragedy in Praed Street. City man found poisoned in Empty House”—such was the general trend of their headlines. And Praed Street, which had begun to breathe again during the respite of the past month, felt once more the cold touch of almost superstitious horror. The killer was abroad again, unknown, unrecognized, and no man could tell when he might feel the dread hand of death upon his shoulder. Inspector Whyland, walking through Praed Street that evening about ten o’clock, heard a cheerful voice bid him good evening, and turned to find Mr. Ludgrove by his side. “Hullo, Mr. Ludgrove!” he exclaimed. “I called at your place just now, and found it shut up. I thought you were away.” “I have been taking my usual evening stroll,” replied the herbalist. “Won’t you come in? I’m on my way home now.” With scarcely a moment’s hesitation, Whyland accepted the invitation. There was always the chance that the herbalist might make some suggestion which would throw light on this latest problem. He waited until they were seated in the familiar back room before he asked the inevitable question. “You’ve heard what happened here this morning, I suppose?” “I have, indeed,” replied Mr. Ludgrove gravely. “The papers contain little beyond the bare facts, but I gather that this unfortunate Mr. Martin was undoubtedly murdered?” “I’m afraid so,” replied the Inspector. “And I fancy by the same hand which committed the previous murders. We found a typed letter on him, suggesting that he should call at Number 407, which had been posted in this district, and there was a counter bearing the number IV lying by his side. You don’t happen to know anything about this Mr. Martin, I suppose?” Mr. Ludgrove shook his head. “I understand that he left Praed Street fifteen years ago,” he replied. “That was long before I came here. In those days I was leading a very quiet life in Devonshire.” He paused, and a curious look of sadness came into his eyes, as of some painful memory. Then he continued briskly, as if ashamed of his momentary lapse. “I daresay that Mr. Copperdock remembers him, he has a wonderful memory for everybody who has ever lived in the neighbourhood.”