"Exactly. He was on the verge of discovering some way of operating for throat cases with complete success. You can imagine how excited he was over his discovery. Unfortunately the patient he experimented on died under the operation, not because the light went out or any nonsense of that kind, but from failure of the heart's action owing to excitement. Heritage had no sleep for a fortnight, and he broke down altogether. For months he was really mad, and when his senses came back to him he had that hallucination. Some day it will go, and some day Heritage will take up the dropped threads of his discovery and the world will be all the better for it. And now, will you do me a favour?" "I will do anything that lies in my power." "Then be good enough to let me have a peep at the man who was found half-murdered in my friend David Steel's conservatory. I'm interested in that case." Cross hesitated for a moment. "All right," he said. "There can't be any harm in that. Come this way." Bell strolled along with the air of a man who is moved by no more than ordinary curiosity. But from the first he had made up his mind not to lose this opportunity. He had not the remotest idea what he expected to find, but he had a pretty good idea that he was on the verge of an important discovery. He came at length to the bedside of the mysterious stranger. The man was lying on his back in a state of coma, his breath came heavily between his parted lips. Bell bent low partly to examine the patient, partly to hide his face from Cross. If Bell had made any discovery he kept the fact rigidly to himself. "Looks very young," he muttered. "But then he is one of those men who never grow any hair on their faces. Young as he looks, I should judge him to be at least forty-five, and, if I am not mistaken, he is a man who has heard the chimes at midnight or later. I'm quite satisfied." "It's more than I am," Cross said, when at length he and his visitor were standing outside together. "Look here, Bell, you're a great friend of Steel's, whom I believe to be a very good fellow. I don't want to get him into any harm, but a day or two ago I found this letter in a pocket-book in a belt worn by our queer patient. Steel says the fellow is a perfect stranger to him, and I believe that statement. But what about this letter? I ought to have sent it to the police, but I didn't. Read it." And Cross proceeded to take a letter from his pocket. It was on thick paper; the stamped address given was "15, Downend Terrace." There was no heading, merely the words "Certainly, with pleasure, I shall be home; in fact, I am home every night till 12.30, and you may call any time up till then. If you knock quietly on the door I shall hear you.--D.S." "What do you make of it?" Cross asked.