The CitÉ Frochot is shut in by low stone walls, topped by grating round which creepers intertwine.

The entry to its main thoroughfare, shaded by trees and lined with small private houses, is not supposed to be public, and a porter's lodge to the right of the entrance is intended to enforce its private character.

It was about seven in the evening. As the fine spring day drew to a close, Fandor reached the square of the CitÉ. For an hour past the journalist had been wholly engaged in keeping track of the famous Loupart, who, after leaving the saloon, had sauntered up the Rue des Martyrs, his hands in his pockets and a cigarette in his mouth.

Fandor allowed him to pass at the corner of the Rue Claude, and from there on kept him in view.

Juve had completely disappeared.

As Loupart, followed by Fandor, was about to enter the CitÉ Frochot, an exclamation made them both turn.

Fandor perceived a poorly dressed man anxiously searching for something in the gutter. A curious crowd had instantly collected, and word was passed round that the lost object was a twenty-five-franc gold piece.

Fandor, joining the crowd, was pushed close to the man, who quickly whispered:

"Idiot! Keep out of the CitÉ."

The owner of the gold piece was no other than the detective. Then, under cover of loud complaint, Juve muttered to Fandor, "Let him go! Watch the entrance to the CitÉ!"

"But," objected Fandor in the same key, "what if I lose sight of him?"

"No fear of that. The doctor's house is the second on the right." The hooligan, who had for a moment drawn near the crowd, was now heading straight for the CitÉ.

Juve went on: "In a quarter of an hour at the latest join me again, 27 Rue Victor MassÉ."

"And if Loupart should enter the CitÉ in the meantime?"

"Come straight back to me."

Fandor was moving off when Juve addressed him out loud: "Thank you, kind gentlemen! But as you are so charitable, give me something more for God's sake."

The other drew near the pretended beggar and Juve added:

"If anyone questions you as you pass through, say you are going to Omareille, the decorator's; you'll find me on the stairs."

Some moments later the little crowd had melted away and a policeman, arriving as usual too late, wondered what had been going on.

Fandor carried out Juve's instructions to the letter. Hiding behind a sentry box he kept an eye on the doctor's house, but nothing out of the way happened. Loupart had vanished, although he was probably not far away. When the fifteen minutes were up Fandor left his post and entered No. 27 Rue Victor MassÉ. As he reached the third floor he heard Juve's voice:

"Is that you, lad?"

"Yes."

"The porter didn't question you?"

"I've seen no one."

"All right, come up here."

Juve was seated at a hall window examining Doctor Chaleck's house through a field glass.

"You've not seen Loupart go in?" he inquired as Fandor joined him.

"Not while I was on watch."

"It's well to know one's Paris and have friends everywhere, isn't it?" continued Juve. "It occurred to me quite suddenly that this might be an excellent place from where to follow citizen Loupart's doings. You would have spoiled everything if you had followed him into the CitÉ. That's why I devised my little scheme to hold you back."

"You are right," admitted Fandor, who, the next moment, gave a jump as Juve's hand gripped him hard.

"Look, Fandor! The bird is going into the cage!"

The journalist, excited, saw a figure already familiar to him in the act of slipping into the little garden which separated Dr. Chaleck's house from the main thoroughfare.

The detective went on: "There he goes, skirting the house until he reaches the little door hidden in the wall. What's he up to now? Ah! He's fumbling in his pocket. False keys, of course."

They saw Loupart open the door and make his way into the house.

"What comes next?" inquired Fandor.

"We are going to tighten the net which the silly bird has hopped into," rejoined Juve, as he bolted down the stairs, and added as a precautionary measure: "While I question the porter, you slip by me into the main street. I have every reason to believe that M. Chaleck has been absent for two days, and as soon as I get this information, I shall pretend to go away, and then—the rest is my concern."

Juve's program was carried out in all points.

To his questions, the porter replied:

"Why, sir, I can't really say. I saw Doctor Chaleck go off with his bag and I haven't seen him come back. However, if you care to see for yourself——"

"No, thanks," replied Juve, "I'll return in a few days. But look out, your lamp's flaring!"

As the porter turned to remedy the trouble, Juve, instead of going off to the right, quickly followed the direction Fandor had taken and caught up with the latter just outside Doctor Chaleck's house.

"Now for our plan of campaign," he said. "It's darker now than it will be later when the street lamps are lit and the moon rises. That excellent Josephine sent me a rough plan of the house. You see there are two windows on the ground floor on either side of the hall. Naturally they belong to the dining-room and drawing-room. The window to the right on the first floor is evidently that of the bedroom. On the left, this window with a balcony belongs to the study of our dealer in death! That's where we must plant ourselves. Understand, Fandor?"

The journalist nodded. "I understand."

The two men advanced carefully, holding their breath and halting at every step. To catch the ruffian in the act they must reach the study without giving the alarm.

The first story of Doctor Chaleck's house was only slightly raised above the ground: by the aid of a drain-pipe, Juve and Fandor managed without difficulty to hoist themselves on to the balcony.

"Here's luck," cried Juve. "The study window is wide open!"

After putting on a pair of rubbers and making Fandor remove his boots, the two men entered the room. Juve's first precaution was to test the two halves of the window. Finding that their hinges did not creak, he fastened the latch and drew the curtains.

"We'll risk a light," he whispered, taking out a pocket-lamp, which lit up the room sufficiently to allow him to take his bearings.

The study was elegantly furnished. In the middle was a huge desk piled with papers, reports, and files. To the right of the desk in the corner opposite the window and half hidden by a heavy velvet curtain was the door leading to the landing. A large corner sofa occupied the space of two wall panels. A set of book-shelves covered a whole wall. Here and there cosy armchairs invited meditation.

"I don't see the famous safe," Murmured Fandor.

"That's because your eyes aren't trained," replied the detective. "Look at that corner sofa, topped by that richly carved bracket. Observe the thick appearance of the delicate mahogany panel. You may be quite sure that it hides a solid steel casket which the best tools would have no easy job to cut through. That little moulding you see to the right can be easily pushed aside."

Here Juve, with the precision of an expert, set the woodwork in motion and showed the astonished Fandor a scarcely visible key-hole.

"Now, let's put out the light and hide ourselves behind the curtains. Luckily they are far enough from the window for our presence not to be noticed."

For about an hour the men remained motionless, then, weary of standing, they squatted on the floor. Each had his revolver ready to hand.

Ten had just struck from a distant clock when suddenly a slight sound reached their attentive ears.

The two had whiled away the time of waiting by drilling the curtains with a small penknife. These holes were invisible at a distance, but enabled them to see what was going on in the room.

The noise continued, slow and measured; some one was walking about in the adjacent rooms without any attempt to disguise the sound. Evidently Loupart believed himself quite alone in the house of the absent doctor.

The steps drew nearer, and Fandor, in spite of his courage, felt the rapid beating of his heart. The handle of the door leading from the hall to the study was turned, and some person entered the room.

There was an instant of silence, and then the desk was suddenly lit up. The new-comer had found the switch. But he was not Loupart.

He seemed a man of forty and wore a brown beard, brushed fan-shape; a noticeable baldness heightened his forehead. On his strongly arched nose a double eye-glass was balanced. Suddenly, having looked at the clock which marked half-past eleven, he began to loosen his tie and unbutton his waistcoat and then went out, leaving the study lit as if intending to come back.

"It's Chaleck!" exclaimed Fandor.

"Just so," replied the detective. "And this complicates matters; we may have to protect him as well as his safe."

Indeed, Juve's first impulse was to go straight to Doctor Chaleck, apprise him of the situation, and, under his guidance, search the house thoroughly. But that would have put Loupart on the alert. It would be taking too great a chance. If Juve should lay hands on him outside of Chaleck's house he would have no right to hold him. For the subtle power of Loupart, that well-loved hooligan of the purlieus of Paris, lay in his remaining constantly a source of fear, always a suspect without ever being caught with the goods.

Coming back to his first idea of insuring Chaleck's safety, Juve said to himself: "The doctor is coming back here, that's sure, and we must protect him without his knowing it. That is the best plan for the present."

Sure enough after an absence of ten minutes Chaleck returned to the study and seated himself at his desk. He had now changed into his pajamas.

Time passed.

When the little Empire time piece which decorated the mantel struck three, Fandor, for all his anxiety, could not repress a yawn: the night was long and thus far had been devoid of incidents. From their hiding-place, he and Juve kept an eye on Doctor Chaleck. When did the man sleep?

Nothing in the physician's countenance betrayed the slightest weariness. He examined numerous documents spread out on the desk, and also wrote a letter which he sealed by lighting a candle and melting some wax. He lingered a good twenty minutes afterwards, then finally put out the lights and left the room.

The room was now in total darkness. The journalist and the detective listened a few moments longer as a precaution, but nothing happened to break the hush of the waning night.

Half an hour more and the outlines of the two would be visible on the thin curtains. It was high time to be off.

Fandor and Juve rose with difficulty to their feet, so cramped were their legs from the enforced rigidity.

"What now?" asked Fandor.

"Listen!" Juve abruptly gripped the other's arm as a fresh noise came to their ears. This time it was not the footsteps of a man walking carelessly, but weird creakings, sly gropings. The noise stopped, began again and again stopped. Where did it come from?

"This room is a mass of hangings," muttered Juve.

"It's impossible to locate those sounds or determine their origin."

"You would suppose," began Fandor——

But he stopped short. The door had opened, the light was switched on and Doctor Chaleck appeared once more, probably disturbed in his sleep by the mysterious noises.

Chaleck gave a quick glance round the room, and then, to the consternation of the two men, he took a few steps toward the window, revolver in hand. At this moment dull creakings were heard, apparently coming from the landing. Chaleck turned quickly, and, leaving the door open, went out. An increase of light indicated that the other rooms in the house were being searched, and as the lights were gradually switched off again, it was apparent that Chaleck was concluding his domiciliary visit without having noticed anything abnormal.

The two remained still for an hour longer, although they had heard Chaleck go back to his room and lock himself into it.

Meantime the daylight was growing brighter, and in a little while the neighbourhood would be awake.

"We must slip out," decreed Juve, as he turned the hasp of the window with infinite care and set it ajar to reach the balcony.

A few moments later Juve had shed his disguise and the two men drew breath in the middle of the Place Pigalle, having fled ignominiously like common criminals.