The journey back to London was one the details of which were registered with photographic realism in Tarling's mind for the rest of his life. The girl spoke little, and he himself was content to meditate and turn over in his mind the puzzling circumstances which had surrounded Odette Rider's flight.

In the very silences which occurred between the interchanges of conversation was a comradeship and a sympathetic understanding which both the man and the girl would have found it difficult to define. Was he in love with her? He was shocked at the possibility of such a catastrophe overtaking him. Love had never come into his life. It was a hypothetical condition which he had never even considered. He had known men to fall in love, just as he had known men to suffer from malaria or yellow fever, without considering that the same experience might overtake him. A shy, reticent man, behind that hard mask was a diffidence unsuspected by his closest friends.

So that the possibility of being in love with Odette Rider disturbed his mind, because he lacked sufficient conceit to believe that such a passion could be anything but hopeless. That any woman could love him he could not conceive. And now her very presence, the fragrant nearness of her, at once soothed and alarmed him. Here was a detective virtually in charge of a woman suspected of murder — and he was frightened of her! He knew the warrant in his pocket would never be executed, and that Scotland Yard would not proceed with the prosecution, because, though Scotland Yard makes some big errors, it does not like to have its errors made public.

The journey was all too short, and it was not until the train was running slowly through a thin fog which had descended on London that he returned to the subject of the murder, and only then with an effort.

"I am going to take you to an hotel for the night," he said, "and in the morning I will ask you to come with me to Scotland Yard to talk to the Chief."

"Then I am not arrested?" she smiled.

"No, I don't think you're arrested." He smiled responsively. "But I'm afraid that you are going to be asked a number of questions which may be distressing to you. You see, Miss Rider, your actions have been very suspicious. You leave for the Continent under an assumed name, and undoubtedly the murder was committed in your flat."

She shivered.

"Please, please don't talk about that," she said in a low voice.

He felt a brute, but he knew that she must undergo an examination at the hands of men who had less regard for her feelings.

"I do wish you would be frank with me," he pleaded. "I am sure I could get you out of all your troubles without any difficulty."

"Mr. Lyne hated me," she said. "I think I touched him on his tenderest spot — poor man — his vanity. You yourself know how he sent that criminal to my flat in order to create evidence against me."

He nodded.

"Did you ever meet Stay before?" he asked.

She shook her head.

"I think I have heard of him," she said. "I know that Mr. Lyne was interested in a criminal, and that this criminal worshipped him. Once Mr. Lyne brought him to the Stores and wanted to give him a job but the man would not accept it. Mr. Lyne once told me that Sam Stay would do anything in the world for him."

"Stay thinks you committed the murder," said Tarling bluntly. "Lyne has evidently told stories about you and your hatred for him, and I really think that Stay would have been more dangerous to you than the police, only fortunately the little crook has gone off his head."

She looked at him in astonishment.

"Mad?" she asked. "Poor fellow! Has this awful thing driven him ..."

Tarling nodded.

"He was taken to the County Asylum this morning. He had a fit in my office, and when he recovered he seemed to have lost his mind completely. Now, Miss Rider, you're going to be frank with me, aren't you?"

She looked at him again and smiled sadly.

"I'm afraid I shan't be any more frank than I have been, Mr. Tarling," she said. "If you want me to tell you why I assumed the name of Stevens, or why I ran away from London, I cannot tell you. I had a good reason ——” she paused, "and I may yet have a better reason for running away...."

She nearly said "again" but checked the word.

He laid his hand on hers.

"When I told you of this murder," he said earnestly, "I knew by your surprise and agitation that you were innocent. Later the doctor was able to prove an alibi which cannot be shaken. But, Miss Rider, when I surprised you, you spoke as though you knew who committed the crime. You spoke of a man and it is that man's name I want."

She shook her head.

"That I shall never tell you," she said simply.

"But don't you realise that you may be charged with being an accessory before or after the act?" he urged. "Don't you see what it means to you and to your mother?"

Her eyes closed at the mention of her mother's name, as though to shut out the vision of some unpleasant possibility.

"Don't talk about it, don't talk about it!" she murmured, "please, Mr. Tarling! Do as you wish. Let the police arrest me or try me or hang me — but do not ask me to say any more, because I will not, I will not!"

Tarling sank back amongst the cushions, baffled and bewildered, and no more was said.

Whiteside was waiting for the train, and with him were two men who were unmistakably branded "Scotland Yard." Tarling drew him aside and explained the situation in a few words.

"Under the circumstances," he said, "I shall not execute the warrant."

Whiteside agreed.

"It is quite impossible that she could have committed the murder," he said. "I suppose the doctor's evidence is unshakable?"

"Absolutely," said Tarling, "and it is confirmed by the station master at Ashford, who has the time of the accident logged in his diary, and himself assisted to lift the girl from the train."

"Why did she call herself Miss Stevens?" asked Whiteside. "And what induced her to leave London so hurriedly?"

Tarling gave a despairing gesture.

"That is one of the things I should like to know," he said, "and the very matter upon which Miss Rider refuses to enlighten me. I am taking her to an hotel," he went on. "To-morrow I will bring her down to the Yard. But I doubt if the Chief can say anything that will induce her to talk."

"Was she surprised when you told her of the murder? Did she mention anybody's name?" asked Whiteside.

Tarling hesitated, and then, for one of the few times in his life, he lied.

"No," he said, "she was just upset ... she mentioned nobody."

He took the girl by taxi to the quiet little hotel he had chosen — a journey not without its thrills, for the fog was now thick — and saw her comfortably fixed.

"I can't be sufficiently grateful to you, Mr. Tarling, for your kindness," she said at parting "and if I could make your task any easier ... I would."

He saw a spasm of pain pass across her face.

"I don't understand it yet; it seems like a bad dream," she said half to herself. "I don't want to understand it somehow ... I want to forget, I want to forget!"

"What do you want to forget?" asked Tarling.

She shook her head.

"Don't ask me," she said. "Please, please, don't ask me!"

He walked down the big stairway, a greatly worried man. He had left the taxi at the door. To his surprise he found the cab had gone, and turned to the porter.

"What happened to my taxi?" he said. "I didn't pay him off."

"Your taxi, sir?" said the head porter. "I didn't see it go. I'll ask one of the boys."

As assistant porter who had been in the street told a surprising tale. A gentleman had come up out of the murk, had paid off the taxi, which had disappeared. The witness to this proceeding had not seen the gentleman's face. All he knew was that this mysterious benefactor had walked away in an opposite direction to that in which the cab had gone, and had vanished into the night.

Tarling frowned.

"That's curious," he said. "Get me another taxi."

"I'm afraid you'll find that difficult, sir." The hotel porter shook his head. "You see how the fog is — we always get them thick about here — it's rather late in the year for fogs..."

Tarling cut short his lecture on meteorology, buttoned up his coat, and turned out of the hotel in the direction of the nearest underground station.

The hotel to which he had taken the girl was situated in a quiet residential street, and at this hour of the night the street was deserted, and the fog added something to its normal loneliness.

Tarling was not particularly well acquainted with London, but he had a rough idea of direction. The fog was thick, but he could see the blurred nimbus of a street lamp, and was midway between two of these when he heard a soft step behind him.

It was the faintest shuffle of sound, and he turned quickly. Instinctively he threw up his hands and stepped aside.

Something whizzed past his head and struck the pavement with a thud.

"Sandbag," he noted mentally, and leapt at his assailant.

As quickly his unknown attacker jumped back. There was a deafening report. His feet were scorched with burning cordite, and momentarily he released his grip of his enemy's throat, which he had seized.

He sensed rather than saw the pistol raised again, and made one of those lightning falls which he had learnt in far-off days from Japanese instructors of ju-jitsu. Head over heels he went as the pistol exploded for the second time. It was a clever trick, designed to bring the full force of his foot against his opponent's knee. But the mysterious stranger was too quick for him, and when Tailing leapt to his feet he was alone.

But he had seen the face — big and white and vengeful. It was glimpse and guess-work, but he was satisfied that he knew his man.

He ran in the direction he thought the would-be assassin must have taken, but the fog was patchy and he misjudged. He heard the sound of hurrying footsteps and ran towards them, only to find that it was a policeman attracted by the sound of shots.

The officer had met nobody.

"He must have gone the other way," said Tarling, and raced off in pursuit, without, however, coming up with his attacker.

Slowly he retraced his footsteps to where he had left the policeman searching the pavement for same clue which would identify the assailant of the night.

The constable was using a small electric lamp which he had taken from his pocket.

"Nothing here, sir," he said. "Only this bit of red paper."

Tarling took the small square of paper from the man's hand and examined it under the light of the lamp — a red square on which were written four words in Chinese: "He brought this trouble upon himself."

It was the same inscription as had been found neatly folded in the waistcoat pocket of Thornton Lyne that morning he was discovered lying starkly dead.