Doctor Renfrew wasted no time in telling him. “When I examined the deceased, it was apparent to me at once that death had been caused by narcotic poisoning—hydrocyanic acid to be precise. It was impossible to mistake the odour round the lips and mouth. She had had a big dose administered.” Bannister pursed his lips. “How was it administered—any idea? For instance—can’t it be suicide?” The doctor’s reply came quickly and readily. “In my opinion—judging from the position of the body—the poison was given from a small hand-syringe. After locking Branston in, the murderer entered the room through the door here—she heard him—turned in his direction and he used the syringe immediately. Her face would be right in front of him. Quite an easy matter—he had doubtless worked out all the details beforehand.” “Cold-blooded business,” muttered Godfrey. “The kind of man I should take a delight in hanging.” “Any purse or anything with her?” demanded Bannister. “Nothing,” answered the Sergeant. “Everything seems to have gone except the hat and this pair of gloves.” A knock sounded on the door and Doctor Renfrew crossed the room to open it. Ronald Branston stood outside. “May I come in?” he queried. Bannister beckoned to him. “I was just about to send down to you, Mr. Branston,” he commenced, “you must have read my thoughts to arrive so opportunely.” Branston bowed. “A dreadful affair this,” he declared, “dreadful from whatever point of view you look at it. Pretty rotten for me, you know—in the business sense. It sounds frightfully callous, I know, but self-preservation’s the first law of nature. This job isn’t going to do my business any good and every man has to think of himself.” He flushed under his dark skin. Bannister eyed him sternly. “I am Chief-Inspector Bannister,” he said, “of ‘Scotland Yard.’ Sergeant Godfrey has requested my assistance. Tell me exactly what happened.” Branston’s nostrils quivered slightly as he began to tell his story but he rapidly regained control over himself and his words came clearly and without a shade of tremor in his voice. “I can only repeat to you,” he stated, “what I have already told Sergeant Godfrey here. This unhappy lady entered the room in which we are now standing a few minutes before two o’clock this afternoon. I had just attended to a previous patient who was my first of the afternoon. She asked me to perform an extraction. I administered a simple local anæsthetic and extracted a left-hand bicuspid. The lady seemed quite comfortable after the extraction. I gave her the usual glass of water as a mouth-wash—there’s the very tumbler on that stand—just as she must have put it down before she was murdered—and then went along to my work-room. I had a special job on this afternoon as I’ve previously explained to the Sergeant and it’s my customary practice to let a patient alone for a moment or two after an extraction.” “One minute,” broke in Bannister. “Was the extraction a necessary one?”