Jack Masefield paused for Inspector Bates to say more. Possibly the officer was possessed of some brilliant idea, but after the first glance at his face it was easy to see that he was as nonplused as Jack himself. It was only the professional caution that spoke; there was no illumination at the back of the policeman's brain.

"I had hoped that perhaps you had discerned something," Masefield said.

"Not quite that, sir," Bates admitted. "So far I am as much in the dark as you are yourself, but my experience is that nothing is to be gained by haste. What I mean is that a thoughtless movement often destroys a clue of the utmost value. I should like to stand here for a moment and consider my position."

Jack drily remarked that there could be no objection to the course proposed by Inspector Bates. It was very late now; there was nothing to be seen, so that the train of thought of the inspector was not likely to be interrupted. He stood facing the great boarded hoarding with its wealth of gaudy pictorial advertisements, but his face did not lighten, and the moody frown was still on his brow.

"Blessed if I can make anything of it," he said in vexed tones. "Here's a man found dead under the most amazing circumstances. There seems to be no motive for the crime; nothing has been removed from the body so far as we know; the man evidently died where he fell. That he was killed I dare say the medical examination will show."

"So far the crime is commonplace and vulgar enough," Jack Masefield suggested. "Scores of these things happen in London every year. Some are found out, but some remain mysteries to the end of time; but this particular crime seems to be peculiarly terrible. First of all, London for some time has been doubly attentive to the yellow-faced posters. No greater advertising circular has ever appealed to the public. Nostalgo is a personality about as great as some of our leading actors. Still, nobody has really regarded Nostalgo as a living force, and I find him dead on the pavement here right in front of one of his own posters. Is that coincidence or an amazing happening?"

"Both, I should say, sir," Bates replied. "An amazing happening in any case. But to find the man dead in front of one of his own posters may be no more than a coincidence. You see, there are so many Nostalgo posters about."

But Jack was loth to give up his point.

"I admit that," he said; "but the particular poster we find up is a fresh one. It was more or less shot-marked, as I pointed out to you; it was marked much as the body of the dead man was marked. If you remember, I suggested examining the poster by means of a magnifying glass, in the hope of finding some kind of printer's trade-mark, and we come back here for that purpose. We find the poster pasted over with a commonplace advertisement of somebody's mustard. Surely that is not coincidence. For some reason or other the poster was covered by design. It is not the habit of the bill-poster to go about the work at midnight."

"Ah, there you are not altogether correct, sir," Bates exclaimed. He felt that he was on pretty safe ground now. "The working bill-poster is not tied to time. He has a certain amount of work to do, and he does it pretty well when he pleases. Sometimes they have to work very late. For instance, a stock piece put up at a theatre may prove a draw, and the management desire to keep it going for a time. Then there is work late at night for some firm of the paste-pot."

"Quite so, inspector; but does that apply to the harmless, necessary mustard advertisement?"

"Not directly, perhaps. But suppose there had been a sudden rush of new and urgent work, the routine would have fallen behind. Please understand that the bill-poster does not career round in a casual way, sticking up a poster just where it suits his fancy. All these hoardings are rented, and big advertisers contract to have so many sheets displayed every week; in fact, it is a most desultory business. Depend upon it, the bill-poster who so lately posted up that alluring mustard tin had nothing to do with the business."

It was all so logical and conclusive that Jack was compelled to drop further argument. At the same time, it seemed rather foolish to stand there doing nothing.

"Look here," he said, struck by a sudden idea; "why not pull that mustard poster down, and get at the real source of the truth. The paper is still wet, and I dare say we might find a ladder behind the hoarding. Let us pull it down, and take the whole thing to the police-station and examine it at our leisure."

There was no objection to this, as Bates was bound to admit. It was a very easy matter to find a way behind the hoarding and secure the firmest of many ladders. A short one was sufficient for the purpose, and very soon the great sheet that contained the mustard advertisement was pulled off the wooden hoarding and lay in a heap on the pavement. In the place of it, fresh and strong, was the yellow face of Nostalgo. Jack took the inspector's lamp and regarded the poster carefully by the magnifying glass. But there was no imprint to be seen, nothing to lead to the identity of the firm who printed the placard.

"I can make nothing whatever of it," Masefield was fain to admit at last. "There are the shot holes plainly marked, as if somebody had used an air-gun or a pea-rifle. Beyond that I can see absolutely nothing of the slightest significance. The best thing for us to do is to see the contractor who has the job in hand in the morning, and get him to saw the poster out of the wooden hoarding for you. The strong light of day may make a difference; but I am not as yet absolutely satisfied that that mustard poster was placed exactly on the top of the yellow face quite by accident."

Bates did not contest the point. He was getting tired and sleepy, and it was very late. "Very well," he said, "we will return to the police station in Shannon Street and have another look at the dead man. It is just possible we may find something there. At the same time, it may be just as well to be on the safe side. I'll get one of my men to come here and keep an eye on the hoarding to-night. It is on the cards that he may see something suspicious. I'll send a plain clothes man here to watch."

As Bates blew softly on his whistle a constable turned up and saluted. He was to stay where he was until relief came, Bates explained. Then he and Jack Masefield went off in the direction of Shannon Street station. The place was perfectly quiet; nobody had been brought in lately; there was no sign of the tragedy here. In a rack near the back, lighted by a skylight some six feet from the ground, lay the murdered body of the man with the yellow face. The malignant look had gone from his face; he seemed calm and placid. As Jack bent over him it seemed to him that there was a movement of the heart. He pointed this out to the inspector, who shook his head.

"People not accustomed to these things often make the same mistake," he said. "I have heard witnesses swear that the body of this or that man was not bereft of life, and in this belief they have been quite certain. Then a doctor comes along and proves beyond a doubt that death has taken place perhaps five or six hours before. Muscular action is what probably deceives people. That poor fellow is dead enough."

Masefield did not argue the matter. It was a sickening business, and he felt that he would gladly see the end of it. Not so Bates, who was inured to this kind of thing. Very rapidly and skilfully he went over the body in search of anything that might be likely to lead to the identification of the deceased. But the pockets were doubtless empty; there was no watch or chain, or purse, no marking on the linen.

"Not even a laundry mark?" Jack suggested. "If my reasoning is correct, a laundry mark has frequently proved of the greatest assistance."

"No mark whatever," said Bates. "The shirt, for instance, is of ordinary make, the class of thing that one buys ready-made at a shop, and which has usually its maker's mark on. There has been a mark of some kind on the neck band, but it looks as if it had been blocked out with chemicals. See how much whiter and thinner the neck band is. We are simply wasting our time here."

Jack said nothing; he could only shake his head sadly. The more the mystery came to be probed the more maddening did it become. A close investigation of the clothing presented as little result; there was nothing even about the boots to prove where they had been made. If the man was a criminal, and his general air suggested that, he had taken the most amazing precaution to prevent identification in case of accidents. Jack looked at the clear, dark features. This was no man to take anybody into his confidence. Success or failure, or crime, must all be undertaken alike alone and unaided. This face would never have led anybody to rejoice with him in good fortune, or sympathize with him in failure.

"Well, I think I had better be getting to my rooms," Masefield said. "I have given you my name and address. I'll come round to-morrow and see if you have made anything out of the poster in the daylight. One thing is pretty certain--there should be no difficulty, if a determined effort is made, to discover the people who printed the picture of the yellow face. There are not many firms in this country capable of such work."

"There is the Continent," Bates suggested. "I'm afraid that it will be very much like looking for a needle in a hayrick. Still----"

What deep philosophical remark Bates was going to make Masefield was not destined to hear, for at the same moment there was the sound of a sudden disturbance in the office beyond. The hoarse voice of a sergeant was heard demanding to know what this little game meant, there was a groan, and the collapse of a heavy body on the floor. Bates strode into the office.

"What is all this row about?" he demanded.

"It's Gregory, sir," the sergeant replied. "Went off half-an-hour ago on some special work for you, or so he said,and here's he back as drunk as a lord; regularly collapsed on the floor, he did. It's not the first time, either."

A sudden suspicion burst upon Masefield. He knelt by the side of the plain clothes man and felt his heart. There was a peculiar red mark round the man's neck as if something had been pulled very tightly round it.

"The man is no more drunk than I am," Jack said. "He has been attacked, and his breath is wholly free from any suspicion of drink. Look at that mark round his neck."

Very slowly the prostrate man struggled to a sitting position. When the fact had once been ascertained that there was no suggestion of intoxication, brandy was administered to him. He had a strange story to tell. He was carrying out instructions when suddenly somebody came behind him and placed a rope round his neck. Before he could recover himself he was partially strangled; he lost consciousness and lay on the pavement. When he came to himself again he was quite alone. He had managed to struggle back to the station, and once there had collapsed on the floor. Robbery was not the motive, for he had lost nothing.

"It's all part of the same mystery," Jack decided. "Something was going on behind that hoarding, and the criminals did not want the policeman to see. I shall walk back to my rooms that way. No, you had better not come along, inspector, in case you are spotted. I shall just walk very coolly by and keep my eye on that hoarding. Good-night!"

There was nothing more to be done, so Masefield was allowed to depart. He had ample food for thought as he walked along the deserted streets. He came at length to the great hoarding where the poster had stood. He stopped just for a moment, almost too amazed to move; then he forced himself to go forward again. For the striking Nostalgo poster was gone. It had been sawn neatly out of the boards of the hoardings leaving a blank square eye in its place!