Juve had spoken in a tone of command that brooked no reply. His keen eyes seemed to pierce through Paul and read his inmost soul. The winking light of the street lamp shed a wan halo round the lad, who obviously wanted to move away from its radius, but Juve held him fast.

"Come now, answer! You are Charles Rambert, and you were Mademoiselle Jeanne?"

"I don't understand," Paul declared.

"Really!" sneered Juve. He hailed a passing cab. "Get in," he ordered briefly, and pushing the lad in before him he gave an address to the driver, entered the cab and shut the door. Juve sat there rubbing his hands as if well pleased with his night's work. For several minutes he remained silent, and then turned to his companion.

"You think it is clever to deny it," he remarked, "but do you imagine it isn't obvious to anyone that you are Charles Rambert, and that you were disguised as Mademoiselle Jeanne?"

"But you are wrong," Paul insisted. "Charles Rambert is dead."

"So you know that, do you? Then you admit that you know whom I am talking about?"

The lad coloured and began to tremble. Juve looked out of the window, pretending not to notice him, and smiled gently. Then he went on in a friendly tone. "But you know it's stupid to deny what can't be denied. Besides, you should remember that if I know you are Charles Rambert I must know something else as well; and therefore——"

"Well, yes," Paul acknowledged, "I am Charles Rambert, and I was disguised as Mademoiselle Jeanne. How did you know it? Why were you at the Saint-Anthony's Pig? Had you come to arrest me? And where are you taking me now—to prison?"

Juve shrugged his shoulders.

"You want to know too much, my boy. Besides, you ought to know Paris, and so ought to be able to guess where I told the driver to go, merely by looking at the streets we are passing through."

"That is exactly what frightens me," Charles Rambert replied. "We are on the quays, near the Law Courts."

"And the Police Station, my son. Quite so. Now it's quite useless to make a scene: you will gain nothing by attempting to get away. You are in the hands of justice, or rather in my hands, which is not quite the same thing, so come quietly. That is really good advice!"

A few minutes later the cab stopped at the Tour Pointue which has such melancholy associations for so many criminals. Juve alighted and made his companion alight as well, paid the driver, and walked up the staircase to the first floor of the building. It was daylight now, and the men were coming on duty; all of them saluted Juve as he walked along with his trembling captive. The detective went down one long passage, turned into another, and opened a door.

"Go in there," he ordered curtly.

Charles Rambert obeyed, and found himself in a small room the nature of which he recognised immediately from the furniture it contained. It was the measuring room of the anthropometric service. So what he feared was about to happen: Juve was going to lock him up!

But the detective called out in a loud tone: "Hector, please!" and one of the men who remained on duty in the department, in case they were required by any of the detective inspectors to find the records of any previously convicted criminal, came hurrying in.

"Ah, M. Juve, and with a bag too! So early? You think he has been here before?"

"No," said Juve in a dry tone that put a stop to further indiscreet questions. "I don't want you to look up my companion's record, but to take his measurements, and very carefully too."

The man was somewhat surprised at the order, for it was not usual to be asked to do such work at so very early an hour. He was rather irritable too at being disturbed from the rest he was enjoying, and it was very curtly that he spoke to Charles Rambert.

"Come here, please: the standard first: take off your boots."

Charles Rambert obeyed and stood under the standard of measurement, and then, as the assistant ordered him, he submitted to having his fingers smeared with ink so that his finger prints might be taken, to being photographed, full face and in profile, and finally to having the width of his head, from ear to ear, measured with a special pair of caliper compasses.

Hector was surprised by his docility.

"I must say your friend is not very talkative, M. Juve. What has he been up to?" and as the detective merely shrugged his shoulders and did not reply, he went on: "That's done, sir. We will develop the negatives and take the prints, and recopy the measurements, and the record shall be classified in the register in a couple of hours."

Charles Rambert grew momentarily more scared. He felt that he was definitely arrested now. But Juve left the arm-chair in which he had been resting, and coming up to him laid his hand upon his shoulder, speaking the while with a certain gentleness.

"Come: there are some other points as to which I wish to examine you." He led him from the anthropometric room along a dark corridor, and presently taking a key from his pocket, opened a door and pushed the lad in before him. "Go in there," he said. "This is where we make the dynamometer tests."

A layman looking round the room might almost have supposed that it was merely some carpenter's shop. Pieces of wood, of various shapes and sizes and sorts, were arranged along the wall or laid upon the floor; in glass cases were whole heaps of strips of metal, five or six inches long, and of varying thickness.

Juve closed the door carefully behind him.

"For pity's sake, M. Juve, tell me what you are going to do with me," Charles Rambert implored.

The detective smiled.

"Well, there you ask a question which I can't answer off-hand. What am I going to do with you, eh? That still depends upon a good many things."

As he spoke Juve tossed his hat aside and, looking at a rather high kind of little table, proceeded to remove from it a grey cloth which protected it from dust, and drew it into the middle of the room. This article was composed of a metal body screwed on to a strong tripod, with a lower tray that moved backwards and forwards, and two lateral buttresses with a steel cross-piece firmly bolted on to them above. Upon this framework were two dynamometers worked by an ingenious piece of mechanism. Juve looked at Charles Rambert and explained.

"This is Dr. Bertillon's effraction dynamometer. I am going to make use of it to find out at once whether you are or are not deserving of some little interest. I don't want to tell you more just at present." Juve slipped into a specially prepared notch a thin strip of wood, which he had selected with particular care from one of the heaps of material arranged along the wall. From a chest he took a tool which Charles Rambert, who had had some intimate experience of late with the light-fingered community, immediately recognised as a jemmy. "Take hold of that," said Juve, and as Charles took it in his hand he added: "Now put the jemmy into this groove, and press with all your force. If you can move that needle to a point which I know, and which it is difficult but not impossible to reach, you may congratulate yourself on being in luck."

Stimulated by this encouragement from the detective, Charles Rambert exerted all his force upon the lever, only afraid that he might not be strong enough. Juve stopped him very soon.

"That's all right," he said, and substituting a strip of sheet-iron for the strip of wood, he handed another tool to the lad. "Now try again."

A few seconds later Juve took a magnifying lens, and closely examined both the strip of metal and the strip of wood. He gave a little satisfied click with his tongue, and seemed to be very pleased.

"Charles Rambert," he remarked, "I think we are going to do a very good morning's work. Dr. Bertillon's new apparatus is an uncommonly useful invention."

The detective might have gone on with his congratulatory monologue had not an attendant come into the room at that moment.

"Ah, there you are, M. Juve: I have been looking for you everywhere. There is someone asking for you who says he knows you will receive him. I told him this was not the proper time, but he was so insistent that I promised to bring you his card. Besides, he says you have given him an appointment."

Juve took the card and glanced at it.

"That's all right," he said. "Take the gentleman into the parlour and tell him I will be with him in a minute." The attendant went out and Juve looked at Charles Rambert with a smile. "You are played out," he said; "before we do anything else common humanity requires that you should get some rest. Come, follow me; I will take you to a room where you can throw yourself on a sofa and get a sleep for a good hour at least while I go and see this visitor." He led the lad into a small waiting-room, and as Charles Rambert obediently stretched himself upon the sofa, Juve looked at the pale and nervous and completely silent boy, and said with even greater gentleness: "There, go to sleep; sleep quietly, and presently——"

Juve left the room, and called a man to whom he gave an order in a low tone.

"Stay with that gentleman, please. He is a friend of mine, but a friend, you understand, who must not leave this place. I am going to see some one, but I will come up again presently," and Juve hurried downstairs to the parlour.

The visitor rose as the door opened, and Juve made a formal bow.

"M. Gervais Aventin?" he said.

"M. Gervais Aventin," that gentleman replied. "And you are Detective-Inspector Juve?"

"I am, sir," the detective answered, and pointing his visitor to a chair he took a seat himself at a small table littered with official documents.

"Sir," Juve began, "I ventured to send you that pressing invitation to come to Paris to-day, because from enquiries I had made about you, I was sure that you were a man with a sense of duty, who would not resent being put to inconvenience when it was a question of co-operating in a work of justice and of truth."

The visitor, a man of perhaps thirty, of somewhat fashionable appearance and careful though quiet dress, manifested much surprise.

"Enquiries about me, sir? And pray, why? I must confess that I was very much astonished when I received your letter informing me that the famous Detective-Inspector Juve wished to see me, and at first I suspected some practical joke. On consideration I decided to obey your summons without further pressing, but I did not imagine that you would have made any enquiries about me. How do you know me, may I ask?"

Juve smiled.

"Is it the fact," he enquired, instead of replying directly, for like the good detective that he was, intensely keen on his work, he enjoyed mystifying people with whom he conversed, "is it the fact that your name is Gervais Aventin? A civil engineer? The possessor of considerable private means? About to be married? And that lately you made a short journey to Limoges?"

The young man nodded and smiled.

"Your information is perfectly correct in every particular. But I do not yet understand what crime of mine can have subjected me to these enquiries on your part."

Juve smiled again.

"I wondered, sir, why you vouchsafed no answer to the local enquiries which have been made at my instance, to the advertisements which I have had inserted in the papers, in which I discreetly made it known that the police wanted to get into communication with all the passengers who travelled first class, in the slow train from Paris to Luchon, on the night of the 23rd of December last."

This time the young man looked anxious.

"Great Scott!" he exclaimed, "are you in the employment of my future father-in-law?"

Juve burst into a roar of laughter.

"First acknowledge that you did travel by that train on that night: that you got into it at Vierzon, where you live and where you are going to be married; and that you were going to Limoges to see a lady—and that you did not want your fiancÉe's family to know anything about it."

Gervais Aventin pulled himself together.

"I had no idea that the official police undertook espionage of that sort," he said rather drily. "But it is true, sir, that I went to Limoges—my last post before I was appointed to Vierzon—to take a final farewell to a lady. But since you are so accurately informed about all this, since you even know what train I went by, a train I deliberately chose because in little places like Vierzon so much notice is taken of people who travel by the express, you must also know——"

Juve checked him with a wave of the hand.

"A truce to jesting," he said; "excuse me, sir, I was only amusing myself by observing once more how quickly decent people, who have a little peccadillo on their conscience, are disturbed when they think they have been found out. Your love affairs do not matter to me, sir; I don't want to know if you have a lady friend, or not. The information I want from you is of a very different nature. Tell me simply this: in what circumstances did you make that journey? What carriage did you get into? Who travelled with you in that carriage? I am asking you because, sir, I have every reason to believe that you travelled that night with a murderer who committed a crime of particular atrocity, and I think you may be able to give me some interesting information."

The young man, who had been looking grave, smiled once more.

"I would rather have that than an enquiry into my defunct love affairs. Well, sir, I got into the train at Vierzon, into a first-class carriage——"

"What kind of carriage?"

"One of the old-fashioned corridor carriages; that is to say, not a corridor communicating with the other carriages, but a single carriage with four compartments, two in the middle opening on to the corridor, and two at the ends communicating with the corridor by a small door."

"I know," said Juve; "the lavatory is in the centre, and the end compartments are like the ordinary noncorridor compartments, except that they have only seven seats, and also have the little door communicating with the narrow passage down one side of the carriage."

"That's it. I got into the smoking compartment at the end."

"Don't go too quick," said Juve. "Tell me whom you saw in the various compartments. Let us go even farther back. You were on the platform, waiting for the train; it came in; what happened then?"

"You want to be very precise," Gervais Aventin remarked. "Well, when the train pulled up I looked for the first-class carriage; it was a few yards away from me, and the corridor was alongside the platform. I got into the corridor and wanted to choose my compartment. I remember clearly that I went first to the rear compartment, the last one in the carriage. I could not get into that, for the door opening into it from the corridor was locked."

"That is correct," Juve nodded. "I know from the guard that that compartment was empty. What did you do then?"

"I turned back and, passing the ladies' compartment and the lavatory, decided to take my seat in the one next it communicating with the corridor. But luck was against me: a pane of glass was broken and it was bitterly cold there; so I had to fall back on the only compartment left, the smoking one towards the front of the train."

"Were there many of you there?"

"I thought at first that I was going to have a fellow-traveller, for there was some luggage and a rug arranged on the seat. But the passenger must have been in the lavatory, for I didn't see him. I lay down on the other seat and went to sleep. When I got out of the train at Limoges, my fellow-traveller must have been in the lavatory again, for I remember quite distinctly that he was not on the opposite seat. I thought at the time how easy it would have been for me to steal his luggage and walk off with his valise: nobody would have seen me."

Juve had listened intently to every word of the story. He asked for one further detail with a certain anxiety in his tone.

"Tell me, sir, when you woke up did you have any impression that the baggage arranged on the seat opposite yours had been disturbed at all? Might the traveller, whom you did not see, have come in for a sleep while you yourself were asleep?"

Gervais Aventin made a little gesture of uncertainty.

"I can't answer in the affirmative, M. Juve. I did not notice that; and, besides, when I got into the compartment, the shade was pulled down over the lamp, and the curtains were drawn across the windows. I hardly saw how the things were arranged. And then, when I got out at Limoges I was in a hurry, and only thought about finding my ticket and jumping on to the platform. But I do not think the other fellow did take his place while I was asleep. I did not hear a sound, and yet I did not sleep at all heavily."

"So you travelled in a first-class compartment in the slow train from Paris to Luchon on the night of the 23rd of December, and in that compartment there was the luggage of a traveller whom you did not see—who may not have been there?"

"Yes," said Gervais Aventin, and, as the detective sat silent for a moment, he enquired: "Is my information too vague to be of any use to you?"

Juve was wondering inwardly why the dickens Etienne Rambert was not in that compartment when, according to the depositions of the guard, he must have been there; but he said nothing of this. Instead, he said:

"Your information is most valuable, sir. You have told me everything I wanted to know."

Gervais Aventin displayed still more surprise.

"Well," he said, "by way of return, M. Juve, tell me something which puzzles me. How did you know I travelled by that train that night?"

The detective drew out his pocket-book, and from an inner pocket produced a first-class ticket, which he held out to the engineer.

"That is very simple," he replied. "Here is your ticket. I wanted to know exactly who everyone was who travelled in that first-class compartment, so I sent for all the first-class tickets which were given up by passengers who left the train at the different stations. That's how I got yours: it had been issued at Vierzon, the station where you got in, so I interrogated the clerk at the booking-office who gave me a description of you; then I sent down an inspector to Vierzon to make discreet enquiries, and he got me all the information I required. All I had to do then was to write and ask you to come here to-day; and the regrettable story of your broken relations with the lady was an ample guarantee to me that you would be punctual at the appointment!"