Colwyn had rooms in the upper part of a block of buildings on Ludgate Hill, looking down on the Circus, above the rookery of passages which burrow tortuously under the railway arches to Water Lane, Printing House Square, and Blackfriars. It was a strange locality to live in, but it suited Colwyn. It was in the thick of things. From his windows, high up above the roar of the traffic, he could watch the ceaseless flow of life eastward and westward all day long, and far into the night.

No other part of London offered such variety and scope in the study of humanity. The City was stodgy, the Strand too uniform, Piccadilly too fashionable, and the select areas for bachelor chambers, such as the Temple and Half Moon Street, were backwaters as remote from the roaring turbulent stream of London life as the Sussex Downs or the Yorkshire Moors.

In addition to these things, the spot offered a fine contrast in walks to suit different moods. There was that avenue of wizardry, Fleet Street, whose high-priests and slaves juggled with the news of the world; there was the glitter of plate-glass fronts between the Circus and St. Paul's, the twilight stillness of the archway passages and their little squeezed shops, the isolation of Play House Yard and Printing House Square, the bustle of Bridge Street, and the Embankment. From his window Colwyn could see the City shopgirls feeding the pigeons of St. Paul's around the statue of Queen Anne.

To Colwyn, London was the place of adventures. He had lived in New York and Paris, but neither of these cities had for him the same fascination as the sprawling giant of the Thames. Paris was as stimulating and provocative as a paid mistress, but palled as quickly. In New York mysteries beckoned at every street corner, but too importunately. Neither city was sufficiently discreet for Colwyn's reticent mind. But London! London was like a woman who hid a secret life beneath an austere face and sober garments. Underneath her air of prim propriety and calm indifference were to be found more enthralling secrets than any other city of the world could reveal. It was emblematic of London that her mysteries, in their strangest aspects and phases, preserved the air of ordinary events.

Colwyn saw nothing extraordinary in this. To him Life seemed so perpetually inconsistent that there could be nothing inconsistent in any of its events. It was to his faith in this axiom, expressed after his own paradoxical fashion, that he partly owed some of those brilliant successes which had stamped him as one of the foremost criminal investigators of his day. He never rejected a story on the score of its improbability. He had seen so many unusual things in his career that he once declared that it was the unforeseen, and not the expected, which occurs most frequently in this strange world of ours. That was, perhaps, partly due to the wide gulf between human ideals and actions, but, whatever the reason, Colwyn never lost sight of the fact that the incredible, once it happened, became as commonplace as the meals we eat or the clothes we wear. It seemed to Colwyn that the unexpected happened too frequently to call forth the astonishment with which it was invariably greeted by most people. In his experience, Life was almost too prodigal of its surprises, so much so, indeed, as to be in danger of reaching the limit of its own resources. But he consoled himself, whimsically enough, with the belief that such an event was too probable ever to happen.

It was nearly eleven o'clock at night, and Colwyn, getting up from a table where he had been busily writing, walked to the window and looked down on the deserted street beneath. It was a nightly custom of his. He lived, as he worked, alone, attended only by a taciturn manservant who had been with him for many years. He accepted with characteristic philosophy the view that a man who spent his time unveiling shameful human secrets had no right to share his life with anybody. Even the articles of furniture of his lonely rooms, if endowed with any sort of entity, might have worn a furtive air in their consciousness of the secrets they had heard whispered in their owner's ears by those who had sought his counsel and assistance in their trouble and despair. There had been many such secrets poured forth in those lonely rooms, perched up high above the roar of the London traffic. It was the Confessional of the incredible.

As Colwyn stood at the window, the electric bell of the front door rang sharply through the empty building. Looking down into the street, he saw the figure of a man in the doorway beneath. He glanced at his watch. It was late for a visitor. He walked to the lift at the end of the passage and descended. As he did so, the bell in his rooms once more pealed forth beneath the pressure of an impatient hand.

The visitor, revealed by the light in the hall, was a young man muffled in a thick overcoat for protection against the sharp autumn wind which was blowing along the rain-splashed street. He stepped inside the door as Colwyn opened it, and, glancing at the detective from a pair of dark eyes just visible beneath the flap of his soft felt hat, said:

"Are you Mr. Colwyn?"

"Yes. What can I do for you?"

"I am afraid it is a very late hour for a visit," said the other, brushing the rain drops off his coat as he spoke, "but I should be very glad if you could spare me a little time, late as it is. I have come from the country to see you."

Colwyn nodded without speaking. Strange adventures had come to him at stranger hours. He showed the way to the lift, switched off the electric light he had turned on in the passage, and ascended with his visitor to his rooms. There his companion, with an impulsiveness which contrasted with the detective's quiet composure, again spoke:

"I want your assistance, Mr. Colwyn."

"Will you not be seated?" said the detective, as with a swift glance he took in the external attributes of his young and well-dressed visitor.

"Thank you. I regret to disturb you at such a late hour, but the train I travelled by was greatly delayed by an accident. I thought at first of postponing my visit till the morning, but it is so urgent—to me, at all events—that I determined to try and see you to-night."

"It was just as well that you did. I may be called out of London in the morning."

"Then I am glad that I came. My name is Heredith—Philip Heredith."

Colwyn looked at his visitor with a keener interest. The London newspapers were full of the particulars of the moat-house crime, and had published intimate accounts of the Heredith family, their wealth, social position, and standing in the county. Colwyn, as he glanced at Philip Heredith, came to the conclusion that the London picture papers had been once more guilty of deceiving their credulous readers. The portraits they had published of him in no wise resembled the young man who was now seated opposite him, regarding him with a sad and troubled look.

"I have heard of your great skill and cleverness in criminal investigation, Mr. Colwyn," continued Phil earnestly, "and wish to avail myself of your help. That is the object of my visit."

Colwyn waited for his visitor to disclose the reasons which had brought him, seeking advice. He had followed the newspaper accounts of the murder and police investigations with keen interest. The special correspondents had done full justice to the arrest of Hazel Rath. There is no room for reticence or delicacy in modern journalism, and no reserves except those dictated by fear of the law for libel. Colwyn was therefore aware that Hazel Rath figured as "the woman in the case," and was supposed to have shot the young wife in a fit of jealousy. The newspapers, in publishing these disclosures, had hinted at the existence of previous tender relations between the young husband and the arrested girl, in order to whet the public appetite for the "remarkable revelations" which it was hoped would be brought forward at the trial.

"I have come to consult you about the murder of my wife," continued Phil, speaking with an evident effort. "I should like you to make some investigations."

Colwyn was sufficiently false to his own philosophy of life to experience a feeling which he would have been the first to admit was surprise.

"The police have already made an arrest in the case," he said.

"I believe they have arrested an innocent girl."

As the young man sat there, he looked so worn and ill that Colwyn felt his sympathy go out to him. He seemed too boyish and frail to bear such a weight of tragedy on his shoulders at the outset of his life. His face wore an aspect of despair.

"If you think that a mistake has been made, you had better go to Scotland Yard," said Colwyn.

"I have already spoken to Detective Caldew, but his attitude convinced me that it was hopeless to expect any assistance from Scotland Yard, so I decided to come to you."

"In that case you had better tell me all that you know, if you wish me to help you," said the detective. "In the first place, I wish to hear all the facts of the murder itself. I have read the newspaper accounts, but they necessarily lack those more intimate details which may mean so much. I should like to hear everything from beginning to end."

In a voice which was still weak from illness, Phil did as he was requested, and related the strange sequence of events which had happened at the moat-house on the night of his wife's murder. Those events, as he described them, took on a new complexion to his listener, suggesting a deeper and more complex mystery than the newspaper accounts of the crime.

From the first the moat-house murder had appealed to Colwyn's imagination and stimulated his intellectual curiosity. There was the pathos of the youth and sex of the victim, murdered in a peaceful country home. The terrible primality of murder accords more easily with the elemental gregariousness of slum existence; its horror is accentuated, by force of contrast, in the tender simplicity of an English sylvan setting. Colwyn's chief interest lay in the fact that, although the case against Hazel Rath was as strong as circumstantial evidence could make it, the supposed motive for the crime was weak. But he reflected that there did not exist in human life any motive sufficiently strong to warrant the commission of a crime like murder. Probably no great murder had ever been justified by motive, in the sense that incitement is vindication, though human nature, ever on the alert in defence of itself, was prone to accept such excuses as passion and revenge as adequate motives for destruction. The point which perplexed Colwyn in this particular case was whether the incitement of jealousy was sufficient to impel a young girl, brought up in good social environment, which is ever a conventional deterrent to violent crime, to murder her rival in a sudden gust of passion.

"Now, let me hear your reasons for thinking that the police have made a mistake in arresting Hazel Rath," the detective said, when Phil had concluded his narration of the events of the night of the murder. "The case against her seems very strong."

"Nevertheless, I feel sure she did not do it," said Phil emphatically. "I understand her nature and disposition too well to believe her guilty. I have known her since childhood. She has a sweet and gentle nature."

"I am afraid your personal opinion will count for very little against the weight of evidence," replied Colwyn. "It is impossible to generalize in a crime like murder. My experience is that the most unlikely people commit violent crimes under sudden stress. Unless you have something more to go upon than that, your protestations will count for very little at the trial. Criminal judges know too well that human nature is capable of almost anything except sustained goodness."

It was the same point of view, only differently expressed, that Superintendent Merrington had advanced to Captain Stanhill at the moat-house the evening after the murder.

"I have other reasons for thinking Hazel Rath innocent," replied Phil. "If she had murdered my wife we would have seen her as we rushed upstairs after hearing the scream and shot. She hadn't time to escape."

"What about the window of your wife's room?"

"It is nearly twenty feet from the ground, so that would be impossible."

"How do you account for the brooch being found in your wife's bedroom? Is there any doubt that it belongs to Hazel Rath?"

"It is quite true that the brooch is hers. I gave it to her on her birthday, some years ago. The police think that Hazel is in love with me, and murdered my wife through jealousy. But that is not true. I have known her since she was a little girl, and regarded her as a sister."

Phil uttered these words with a ringing sincerity which it was impossible to doubt. But that statement, Colwyn reflected, did not carry them very far. The speaker might honestly believe that the feeling existing between himself and Hazel Rath was like the affection of brother and sister, but he was speaking for himself, and not for the girl. Who could read the secret of a woman's heart? The real question was, did Hazel Rath love Philip Heredith? There lay a motive for the murder, if she did.

"Does Hazel Rath still refuse to explain how her brooch came to be found in Mrs. Heredith's bedroom and subsequently disappeared?" inquired Colwyn after a short pause.

"I understand that she persists in remaining silent," returned the young man. "Oh, I admit the case seems suspicious against her," he continued passionately, as though in answer to a slight shrug of the detective's shoulders. "It is for that reason I have come to you. I believe her innocent, and I want you to try and establish her innocence."

"I am afraid I must decline, Mr. Heredith." A sympathetic glance of Colwyn's eyes softened the firm tone of the refusal. "Apart from your own belief in Miss Rath's innocence, you have very little to go upon."

"There is more than that to go upon," said Phil. "There is the question of the identity of the revolver. Hazel is supposed to have obtained it from the gun-room."

"I know that from the newspaper reports."

"Yes, but you do not know that the detectives have not been able to establish the ownership of the weapon until to-day. They were under the impression that it belonged to the moat-house, but neither my father nor aunt was able to settle the point. Detective Caldew visited the moat-house to-day to see if I could identify it. I immediately recognized it as the property of Captain Nepcote."

"Who is Captain Nepcote?"

"He is a friend of mine. I knew him in London before I was married. He was a friend of my wife's also. He was one of our guests at the moat-house until the day of the murder."

"Did he leave before the murder was committed?"

"Yes; some hours before."

"Then how did Hazel Rath obtain possession of his revolver?"

"That is what I do not know. I must tell you that the day before the murder some of our guests spent a wet afternoon amusing themselves shooting at a target in the gun-room. They were using Captain Nepcote's revolver. When I told Detective Caldew this, he came to the conclusion that Nepcote must have left it there after the shooting, and Hazel Rath found it when she went to look for a weapon."

"I see. And what is your own opinion?"

"I do not believe it for one moment."

"Why not?"

"For one thing, it strikes me as unlikely that Nepcote would forget his revolver when leaving the gun-room. In any case, the police are taking too much for granted in assuming, without inquiry, that he did. Caldew told me that the question of the ownership of the revolver did not affect the case against Hazel Rath in the slightest degree."

"Do you know whether the revolver was seen by anybody between the time of Captain Nepcote's departure and its discovery in Hazel Rath's possession?"

"I understand that it was not."

"Do you know whether Captain Nepcote took it from the gun-room after the target shooting?"

"That I cannot say. I left the gun-room before the shooting was finished."

"Let me see if I thoroughly understand the position," said Colwyn. "In your narrative of the events of the murder you stated that all the members of the household and the guests were in the dining-room when the murder was committed. Nepcote was not there because he had returned to London during the afternoon. Nevertheless, it was with his revolver that your wife was shot."

"That is correct," said Phil.

"If Nepcote did not leave his revolver in the gun-room the police theory would be upset on an important point, and the case would take on a new aspect. Have you any suspicions that you have not confided to me?"

"I cannot say that I have any particular suspicions," the young man replied. "I do not know what to think, but I should like to have this terrible mystery cleared up. I have not seen Nepcote since the day of the murder to ask him about the revolver. He said good-bye to me before he left, and I understood that he had received a wire from the War Office recalling him to the front. After the murder I was taken ill, as I have told you, and it was not until to-day that I was informed of what happened during my illness."

"I am inclined to agree with you that the case wants further investigation," said Colwyn.

"Then will you undertake it?" asked Phil.

The feeling that he was face to face with one of the deepest mysteries of his career acted as an irresistible call to Colwyn's intellect. He consulted the leaves of his engagement book.

"Yes, I will come," he said.

Phil glanced at his watch.

"I am afraid we can hardly catch the last train to Heredith," he said.

"We will drive down in my car," said Colwyn. "Please excuse me for a few moments."

He left the room, and returned in a few moments fully equipped for the journey.

"Let us start," he said.

His tone was decided and imperative, his movements quick and full of energy. That was wholly like him, once he had decided on his course.