Tarling should have been sleeping. Every bone and sinew in him ached for rest. His head was sunk over a table in his flat. Lyne's diaries stood in two piles on the table, the bigger pile that which he had read, the lesser being those which Tarling had yet to examine.

The diaries had been blank books containing no printed date lines. In some cases one book would cover a period of two or three years, in other cases three or four books would be taken up by the record of a few months. The pile on the left grew, and the pile on the right became smaller, until there was only one book — a diary newer than the others which had been fastened by two brass locks, but had been opened by the Scotland Yard experts.

Tarling took up this volume and turned the leaves. As he had expected, it was the current diary — that on which Thornton Lyne had been engaged at the time of his murder. Tarling opened the book in a spirit of disappointment. The earlier books had yielded nothing save a revelation of the writer's egotism. He had read Lyne's account of the happenings in Shanghai, but after all that was nothing fresh, and added little to the sum of the detective's knowledge.

He did not anticipate that the last volume would yield any more promising return for his study. Nevertheless, he read it carefully, and presently drawing a writing pad toward him, he began to note down excerpts from the diary. There was the story, told in temperate language and with surprising mildness, of Odette Rider's rejection of Thornton Lyne's advances. It was a curiously uninteresting record, until he came to a date following the release of Sam Stay from gaol, and here Thornton Lyne enlarged upon the subject of his "humiliation."

"Stay is out of prison," the entry ran. "It is pathetic to see how this man adores me. I almost wish sometimes that I could keep him out of gaol; but if I did so, and converted him into a dull, respectable person, I should miss these delicious experiences which his worship affords. It is good to bask in the bright sunlight of  his adoration! I talked to him of Odette. A strange matter to discuss with a lout, but he was so wonderful a listener! I exaggerated, the temptation was great. How he loathed her by the time I was through ... he actually put forward a plan to 'spoil her looks,' as he put it. He had been working in the same prison gang as a man who was undergoing a term of penal servitude for 'doing in' his girl that way ... vitriol was used, and Sam suggested that he should do the work.... I was horrified, but it gave me an idea. He says he can give me a key that will open any door. Suppose I went ... in the dark? And I could leave a clue behind. What clue? Here is a thought. Suppose I left something unmistakably Chinese? Tarling had evidently been friendly with the girl ... something Chinese might place him under suspicion...."

The diary ended with the word "suspicion," an appropriate ending. Tarling read the passages again and again until he almost had them by heart. Then he closed the book and locked it away in his drawer.

He sat with his chin on his hand for half an hour. He was piecing together the puzzle which Thornton Lyne had made so much more simple. The mystery was clearing up. Thornton Lyne had gone to that flat not in response to the telegram, but with the object of compromising and possibly ruining the girl. He had gone with the little slip of paper inscribed with Chinese characters, intending to leave the Hong in a conspicuous place, that somebody else might be blamed for his infamy.

Milburgh had been in the flat for another purpose. The two men had met; there had been a quarrel; and Milburgh had fired the fatal shot. That part of the story solved the mystery of Thornton Lyne's list slippers and his Chinese characters; his very presence there was cleared up. He thought of Sam Stay's offer.

It came in a flash to Tarling that the man who had thrown the bottle of vitriol at him, who had said he had kept it for years — was Sam Stay. Stay, with his scheme for blasting the woman who, he believed, had humiliated his beloved patron.

And now for Milburgh, the last link in the chain.

Tarling had arranged for the superintendent in charge of the Cannon Row Police Station to notify him if any news came through. The inspector's message did not arrive, and Tarling went down through Whitehall to hear the latest intelligence at first hand. That was to be precious little. As he was talking there arrived on the scene an agitated driver, the proprietor of a taxicab which had been lost. An ordinary case such as come the way of the London police almost every day. The cabman had taken a man and a woman to one of the West End theatres, and had been engaged to wait during the evening and pick them up when the performance was through. After setting down his fares, he had gone to a small eating-house for a bit of supper. When he came out the cab had disappeared.

"I know who done it," he said vehemently, "and if I had him here, I'd...."

"How do you know?"

"He looked in at the coffee-shop while I was eating my bit of food."

"What did he look like?" asked the station inspector.

"He was a man with a white face," said the victim, "I could pick him out of a thousand. And what's more, he had a brand-new pair of boots on."

Tarling had strolled away from the officer's desk whilst this conversation was in progress, but now he returned.

"Did he speak at all?" he asked.

"Yes, sir," said the cabman. "I happened to ask him if he was looking for anybody, and he said no, and then went on to talk a lot of rubbish about a man who had been the best friend any poor chap could have had. My seat happened to be nearest the door, that's how I got into conversation with him. I thought he was off his nut."

"Yes, yes, go on," said Tarling impatiently. "What happened then?"

"Well, he went out," said the cabman, "and presently I heard a cab being cranked up. I thought it was one of the other drivers — there were several cabs outside. The eating-house is a place which cabmen use, and I didn't take very much notice until I came out and found my cab gone and the old devil I'd left in charge in a public-house drinking beer with the money this fellow had given him."

"Sounds like your man, sir," said the inspector, looking at Tarling.

"That's Sam Stay all right," he said, "but it's news to me that he could drive a taxi."

The inspector nodded.

"Oh, I know Sam Stay all right, sir. We've had him in here two or three times. He used to be a taxi-driver — didn't you know that?"

Tarling did not know that. He had intended looking up Sam's record that day, but something had occurred to put the matter out of his mind.

"Well, he can't go far," he said. "You'll circulate the description of the cab, I suppose? He may be easier to find. He can't hide the cab as well as he can hide himself, and if he imagines that the possession of a car is going to help him to escape he's making a mistake."

Tarling was going back to Hertford that night, and had informed Ling Chu of his intention. He left Cannon Row Police Station, walked across the road to Scotland Yard, to confer with Whiteside, who had promised to meet him. He was pursuing independent inquiries and collecting details of evidence regarding the Hertford crime.

Whiteside was not in when Tarling called, and the sergeant on duty in the little office by the main door hurried forward.

"This came for you two hours ago, sir," he said "We thought you were in Hertford."

"This" was a letter addressed in pencil, and Mr. Milburgh had made no attempt to disguise his handwriting. Tarling tore open the envelope and read the contents:

"Dear Mr. Tarling," it began. "I have just read in the Evening Press, with the deepest sorrow and despair, the news that my dearly Beloved wife, Catherine Rider, has been foully murdered. How terrible to think that a few hours ago I was conversing with her assassin, as I believe Sam Stay to be, and had inadvertently given him information as to where Miss Rider was to be found! I beg of you that you will lose no time in saving her from the hands of this cruel madman, who seems to have only one idea, and that to avenge the death of the late Mr. Thornton Lyne. When this reaches you I shall be beyond the power of human vengeance, for I have determined to end a life which has held so much sorrow and disappointment. — M."

He was satisfied that Mr. Milburgh would not commit suicide, and the information was superfluous that Sam Stay had murdered Mrs. Rider. It was the knowledge that this vengeful lunatic knew where Odette Rider was staying which made Tarling sweat.

"Where is Mr. Whiteside?" he asked.

"He has gone to Cambours Restaurant to meet somebody, sir," said the sergeant.

The somebody was one of Milburgh's satellites at Lyne's Store. Tarling must see him without delay. The inspector had control of all the official arrangements connected with the case, and it would be necessary to consult him before he could place detectives to watch the nursing home in Cavendish Place.

He found a cab and drove to Cambours, which was in Soho, and was fortunate enough to discover Whiteside in the act of leaving.

"I didn't get much from that fellow," Whiteside began, when Tarling handed him the letter.

The Scotland Yard man read it through without comment and handed it back.

"Of course he hasn't committed suicide. It's the last thing in the world that men of the Milburgh type ever think about seriously. He is a cold-blooded villain. Imagine him sitting down to write calmly about his wife's murderer!"

"What do you think of the other matter — the threat against Odette?"

Whiteside nodded.

"There may be something in it," he said. "Certainly we cannot take risks. Has anything been heard of Stay?"

Tarling told the story of the stolen taxicab.

"We'll have him," said Whiteside confidently. "He'll have no pals, and without pals in the motor business it is practically impossible to get a car away."

He got into Tarling's cab, and a few minutes later they were at the nursing home.

The matron came to them, a sedate, motherly lady.

"I'm sorry to disturb you at this hour of the night," said Tarling, sensing her disapproval. "But information has come to me this evening which renders it necessary that Miss Rider should be guarded."

"Guarded?" said the matron in surprise. "I don't quite understand you, Mr. Tarling. I had come down to give you rather a blowing up about Miss Rider. You know she is absolutely unfit to go out. I thought I made that clear to you when you were here this morning?"

"Go out?" said the puzzled Tarling. "What do you mean? She is not going out."

It was the matron's turn to be surprised.

"But you sent for her half an hour ago," she said.

"I sent for her?" said Tarling, turning pale. "Tell me, please, what has happened?"

"About half an hour ago, or it may be a little longer," said the matron, "a cabman came to the door and told me that he had been sent by the authorities to fetch Miss Rider at once — she was wanted in connection with her mother's murder."

Something in Tarling's face betrayed his emotion.

"Did you not send for her?" she asked in alarm.

Tarling shook his head.

"What was the man like who called?" he asked:

"A very ordinary-looking man, rather under-sized and ill-looking — it was the taxi-driver."

"You have no idea which way they went?"

"No," replied the matron. "I very much objected to Miss Rider going at all, but when I gave her the message, which apparently had come from you, she insisted upon going."

Tarling groaned. Odette Rider was in the power of a maniac who hated her, who had killed her mother and had cherished a plan for disfiguring the beauty of the girl whom he believed had betrayed his beloved master.

Without any further words he turned and left the waiting-room, followed by Whiteside.

"It's hopeless," he said, when they were outside, "hopeless, hopeless! My God! How terrible! I dare not think of it. If Milburgh is alive he shall suffer."

He gave directions to the cab-driver and followed Whiteside into the cab.

"I'm going back to my flat to pick up Ling Chu," he said. "I can't afford to lose any help he may be able to give us."

Whiteside was pardonably piqued.

"I don't know if your Ling Chu will be able to do very much in the way of trailing a taxicab through London." And then, recognising something of the other's distress, he said more gently, "Though I agree with you that every help we can get we shall need."

On their arrival at the Bond Street flat, Tarling opened the door and went upstairs, followed by the other. The flat was in darkness — an extraordinary circumstance, for it was an understood thing that Ling Chu should not leave the house whilst his master was out. And Ling Chu had undoubtedly left. The dining-room was empty. The first thing Tarling saw, when he turned on the light, was a strip of rice paper on which the ink was scarcely dry. Just half a dozen Chinese characters and no more.

"If you return before I, learn that I go to find the little-little woman," read Tarling in astonishment.

"Then he knows she's gone! Thank God for that!" he said. "I wonder ——”

He stopped. He thought he had heard a low moan, and catching the eye of Whiteside, he saw that the Scotland Yard man had detected the same sound.

"Sounds like somebody groaning," he said. "Listen!"

He bent his head and waited, and presently it came again.

In two strides Tarling was at the door of Ling Chu's sleeping place, but it was locked. He stooped to the key-hole and listened, and again heard the moan. With a thrust of his shoulder he had broken the door open and dashed in.

The sight that met his eyes was a remarkable one. There was a man lying on the bed, stripped to the waist. His hands and his legs were bound and a white cloth covered his face. But what Tarling saw before all else was that across the centre of the broad chest were four little red lines, which Tarling recognised. They were "persuaders," by which native Chinese policemen secretly extract confessions from unwilling criminals — light cuts with a sharp knife on the surface of the skin, and after ——

He looked around for the "torture bottle," but it was not in sight.

"Who is this?" he asked, and lifted the cloth from the man's face.

It was Milburgh.