DR GUSTAVUS MURRELL lived in Sackville Street, Piccadilly. He was a man of private means, and he possessed a medical practice that brought him in about a thousand a year. One of those pleasant practices, where the lowest fee for looking at a tongue is a guinea, and for an operation fifty.

He was a tall, well-groomed, handsome man of forty-five or so, with a jovial blue eye and a hearty manner. You never would have imagined that one of the chief hobbies of this healthy and happy-looking individual was grubbing in the cesspit of crime. Yet it was.

Only one of his hobbies, for he had several, photography amongst the rest.

Though a dilettante of criminal acts and possessed of a profound penetrative power, as far as human motives were concerned, Dr Murrell was no amateur detective. He studied criminals just as a botanist studies fungi; they interested him, and he felt a sort of sympathy for them, that sympathy which we all feel, more or less, for the things that interest us.

He acted as police surgeon, because, in that position, he was brought into contact with the people who helped to constitute his hobby. But he never helped the police in the least, beyond the assistance that his position bound him in duty to give.

On several occasions he could have given the police a clue that would have helped them considerably in their work, yet he refrained. He was the police surgeon, but he did not feel himself bound to help the police beyond the help that his surgical knowledge was able to give.

In the case of the valet Leloir he did not care twopence whether the result of his investigations brought a criminal to justice or cleared up a mystery.

The thing was outside his province, and he embarked on it because he was a photographer.

Freyberger arrived at Sackville Street about six, and found Dr Murrell at home. The doctor was in his study, going over his case book, and he bade his visitor be seated.

“You have called about the case I saw this morning, I suppose?” said Dr Murrell. “Well, I have done what I said I would do. I have already removed the right eye, stripped the retina, exposed it and got a result; the picture is at present the size of a sixpence; my man is at work on it now; it is being reproduced and magnified enormously, under the rays of a five thousand candle-power arc-light. If you will call again to-night I will show you the ultimate result, larger than a cabinet-sized photograph.”

“You have got a picture?” said Freyberger.

“I have got a picture,” replied the other, “or fancy so, and, as I say, you will be able to see it to-night.”

“What time shall I call?” asked the detective.

“Oh, about ten.”

“The body has been removed to the mortuary?”

“Yes, it was there I took the eye, substituting a glass one. The inquest will be to-morrow, and, of course, the post-mortem. I expect the post-mortem will show that the man had a weak heart.”

“You think he died of heart failure?”

“I have told you already he died of terror; but I think the heart weakness was the secondary cause of his death. I see in the papers that a warrant is out for Sir Anthony Gyde. Have you caught him yet?”

“No,” said Freyberger, “and we never will.”

The other looked surprised.

“I have only skimmed through the report in the paper,” he said. “From it I gather that it is very clearly proved that he has murdered a man up in Cumberland.”

“You have not seen the head, then, that was found in his house in Piccadilly?”

“No, I was from home when they sent for me, and they called the Home Office expert in.”

Freyberger gave him all the details we know, and the doctor sat listening and tapping with his pencil on the desk.

“Well,” he said, when the other had finished, “you seem to have a pretty tangled skein to unravel; what I can show you to-night may help you or not. Call at ten; and now I must take leave of you, for I have another patient to see before dinner.”

Freyberger bowed himself out. He had almost four hours to wait before the appointment, and, having nothing particular to do, he determined to make the best use he could of the time at his disposal, and have dinner.

He first telephoned to the Yard the result of his interview with Dr Murrell, and then betook himself to a cheap restaurant in Soho, where he proceeded to revel in Sauerkraut and beef, served with stewed plums, slices of sausage and other Teutonic delicacies.

Throughout all the varied experiences of his life he had never felt so much excitement as just now, waiting for the result of this sleight of hand photography, this attempt to trick nature out of one of her darkest secrets.

It was exactly ten o’clock when he reached the house in Sackville Street, and was admitted.

The doctor was not at home, but he had given instructions that the detective should be admitted to his private laboratory, there to await him.

It was a large room at the back of the house, built on a space that had once been a yard. It had a top light and something of the general aspect of an artist’s studio.

R?ntgen ray apparatuses, cameras, all sorts of odds and ends lay about, speaking of the occupant’s bent.

Freyberger had not been waiting five minutes when the door opened, and Dr Murrell, in evening dress, entered.

He held a small parcel in his hand.

“Good evening,” he said. “My assistant was called away half an hour ago, and he left the result of his work for me; let’s see what it is.”

He undid the string from the parcel, and disclosed what at first sight appeared to be a large cabinet photograph.

He approached an electric light, bearing it in his hand; in the full glare of the light he examined it intently. Then he whistled softly to himself. He seemed quite lost in contemplation of the thing.

Freyberger, unable to contain his curiosity, came up behind the doctor and gazed over his shoulder at the photograph, mounted upon the card.

It was a large grey-coloured platinotype, showing a blurred and misty picture; it was the picture of a human face.

It was the face, the sight of which had killed, from sheer terror, the valet Leloir.

The arteries of the dead man’s retina had left their trace upon the photograph, but they did not blur the face; their tracery could be seen in the background, forming a sort of halo round the nebulous visage, that held the two gazers with a witchery all its own.

“That is the result,” said the doctor, laying the photograph on a table near by.

Freyberger moistened his lips.

“Scarcely pretty,” said Dr Murrell, taking a cigarette from a box near by and offering his companion one.

“It is a face to give one pause,” said Freyberger, lighting his cigarette in a meditative manner.

“I’m sure of this,” said Dr Murrell, leaning back against the mantelpiece and glancing sideways at the thing on the table, “that half of the impression that thing makes upon me is caused by the fact that I have the knowledge of how it was obtained.

“The fact of finding a man dead of terror and then finding that picture on his retina, is, I think, part of the reason why I feel—pretty sick.”

“It’s bad enough,” said Freyberger, bending over the table and staring at the thing.

“The other part of the reason is the thing itself.”

Freyberger continued gazing without a word.

“You seem in love with it.”

“I am studying it, stripping it of all its accessories. This is the portrait of a human face; it belonged to a person who was in the bedroom of Sir Anthony Gyde just before the death of Leloir; the sight of it killed Leloir, we may presume, from shock.”

“Yes.”

“Well, presumptions are sometimes wrong.”

“Explain yourself.”

“I am studying this face intently; it has all the features of an ordinary human, though very evil, face; in repose one may fancy it repulsive, but not especially alarming, certainly not alarming enough to kill a man from shock.”

“Yes?”

“It is the expression of the thing that constitutes its chief feature.”

“Yes.”

“What is that expression? It is a compound of alarm and hatred.”

“Yes,” said the doctor, coming to the table and glancing at the thing, and then returning to his post at the mantelpiece.

“Yes, I should say that is the expression—or at all events, a very good imitation of it.”

“Well,” went on the other, “from the expression on this face I construct the following hypothesis. Leloir suddenly entered his master’s bedroom and found a stranger there, a stranger to whom the face whose picture we see here belonged. He surprised him, perhaps, committing some act, to which we have no clue; anyhow, he surprised him. Hence the expression.”

“I can understand that causing the expression of alarm. How about the ferocious hatred we see here—”

“Mark you,” said Freyberger, “I did not say terror. I said alarm. If you have ever alarmed a man and been attacked by him, you will understand how closely allied alarm and hatred of the most ferocious description may be. I have experienced the fact several times, I assure you, in the course of my professional work.”

“I can imagine so.”

“Well, granting my supposition,” continued the other, “we may ask ourselves, what was this man doing when Leloir surprised him? It was not the face of the creature that killed Leloir with shock, we may presume, but the act he was committing. What was that act?”

“Trying to murder Gyde, perhaps, since it is known that Gyde was in the bedroom after the secretary heard that scream, which was evidently the scream of Leloir dying.”

“I have quite cast Gyde out of my mind,” said Freyberger. “I have quite come to the conclusion that Gyde has no more to do with this whole case than the child unborn. I am firmly convinced—mind, I say this to you privately—that the only criminal in this case is the man whom Gyde is supposed to have murdered, that is to say, the artist Klein, alias Kolbecker.

“I believe this face to be a portrait of Klein.

“I have no earthly idea yet of the full devilish ingenuity of the thing, but I feel assured that, whoever was murdered in the cottage on the fells of Cumberland, Klein is the murderer. Gyde may be alive, Gyde may be dead, but I feel assured of this, that Klein murdered a man, and has arranged matters so that the public believe that he is the victim and Gyde the assassin. Now I must go, for there is much work to be done. May I take this portrait with me; it is most important?”

“Certainly, if you will return it to me when you have done with it. I want it for my museum.”

“I will return it,” said Freyberger. He did it up in the brown paper, placed it in the pocket of his overcoat, and, bidding Doctor Murrell good night, departed.

In Piccadilly he hailed a cab and drove to Howland Street, to the house he had visited that afternoon.

On the way he reviewed many things in his mind.

He already had a theory. The theory that Gyde was innocent and Klein was the assassin; he had also a suspicion that Gyde was dead.

That this theory and suspicion cast the whole affair into deeper darkness was nothing if they were right.

Just ............