The Empire clock on Juve's desk struck half-past eleven. The detective, having gone over in his mind the course of events just narrated, rose abruptly and tapped Wulf on the shoulder.

"Monsieur Wulf, if you are to remain here you are very welcome to do so; as for me, I'm going out."

Wulf, wakened out of a doze, sat up and stared at Juve, an expression of dawning suspicion in his eyes.

"Where are you going?" he inquired.

Juve, absorbed in his thoughts, did not remark the strange behavior of his colleague. He had settled on a plan of action, which was simply to arrest the Marquis de SÉrac.

"Oh, I'm just going ... for a walk."

"All right, get your hat."

A few moments later the two men hailed a taxi and drove to 247 Rue de Monceau.

During the trip Juve pumped Wulf about his relations with Fandor, and it appeared that the latter had pursued the policy of making Wulf drunk upon every occasion. Doubtless, the detective reasoned, it was thus that Fandor was enabled to escape for an hour, during which time the substitution had been effected. Wulf explained how he had found the King near the fountains in the Place de la Concorde, and Juve realized that in some way or other the King and the fountains were mysteriously connected.

In his turn, Wulf plied Juve with questions as to what he had done during his stay at Glotzbourg.

What sort of welcome had he received from M. Heberlauf?

How had the arrest of FantÔmas been effected?

How had the monster died?

The detective, naturally, had no intention of enlightening Wulf as to the truth.

He therefore answered in monosyllables, annoyed by the turn the conversation had taken. In fact, as the questions became more pressing, it flashed through Juve's mind that the stupid officer was actually beginning to suspect him of being FantÔmas. As the taxi neared its destination Juve suddenly put his head out of the window and cried with an oath to the chauffeur:

"Follow that automobile which is just starting and don't lose sight of it!"

Wulf turned inquiringly:

"It's the Marquis de SÉrac."

"Well, what of it?"

"Why, is he the man we are after?" Then turning again to the chauffeur:

"Have you plenty of gasoline?"

"Enough to run a hundred miles, Monsieur."

The chase began at the Boulevard de Courcelles, continued through the Place de l'Etoile and the Avenue de la Grande ArmÉe. The two taxis, of the same horsepower, kept an equal pace, but the Marquis de SÉrac's chauffeur seemed the smarter man. At any rate, he was the more daring. He dodged in and out of the traffic and began to gain on his pursuers.

"He's taking us to the Bois," growled Juve, as they made a turn to the left after passing the fortifications, before the BarriÈre de Neuilly. The pace increased in the back streets and then, suddenly, the taxi of the Marquis de SÉrac disappeared!

It had turned sharply down a narrow street.

At the risk of his neck, the detective sprang out of his taxi and rushed round the corner, just in time to hear a door bang to.

Wulf now joined him.

"We have wasted our time, my dear Juve. The taxi we have been following was empty. It made a circuit and passed me just now."

"Just what I expected!" cried Juve, "our man got out of it ... he is still here."

Juve took out his revolver, and then an exclamation of surprise escaped his lips. Fifty yards away, a figure appeared, vague and dressed in white.

"What the devil does that mean? I've been following the Marquis de SÉrac, of that I'm sure, and now I find this other one." Then turning to Wulf, he gripped him by the arm. "You see that individual, well, he is the Primitive Man Ouaouaoua."

Taking the utmost precaution, Juve and Wulf followed the enigmatic Ouaouaoua for over an hour. The singular meeting had given the detective food for thought. This man had figured prominently at the ceremony of the Singing Fountains; again, he had been foremost in the demonstration of the mob against the King outside the Royal Palace. It was now that a suspicion came to Juve's mind, that this venerable beard and white woollen robe concealed the person of the Marquis de SÉrac.

"Whatever happens," he muttered, "I must get to the bottom of this. While it would be quite easy to bring him down with a shot from my revolver, yet, once dead, I could get no information from him."

They arrived at the corner of the Boulevard Malesherbes and the Avenue de Villiers, and Juve's excitement grew, for he knew that not far away was the America Hotel, where Lady Beltham had put up under the name of the Grand Duchess Alexandra. Ah! If it were possible to connect the Primitive Man with her! In that case he would not hesitate to arrest them both, although he suspected that FantÔmas's mistress would be more ready to give him up than to shield him.

But Ouaouaoua brusquely made a right-about face and headed toward the Boulevard des Batignolles.

"Are we going to keep this up much longer?" inquired Wulf, who by this time was breathless and weary.

"You can go if you like," growled Juve without turning his head. In his intense absorption, Juve failed to notice the menacing and ironical look the officer directed at him.

Ouaouaoua now turned down the Rue Notre-Dame-de-Lorette hastening his speed. The two men had some difficulty in keeping up with him. Suddenly he disappeared at the corner of the Rue Saint Lazare and the Rue Lamartine. Juve sprang forward just in time to see the white draped figure vanish down the stairs leading to the underground Station of the Nord-Sud.

The Station was lighted and the ticket windows open. The morning's traffic had begun.

"Have you just seen a queerly dressed man?" he asked one of the porters.

"He has just bought his ticket, Monsieur."

Juve flung down a coin, seized two coupons and without waiting for the change hurried onto the platform. The first morning train was waiting, due to start in five minutes. A quick search through the carriages disclosed the object of Juve's search. He was standing in the first carriage by the door of the driver's compartment. While Juve eyed him eagerly, the Primitive Man in turn was watching the detective.

The conductors and employÉs were standing gossiping by the ticket office, and the station was almost deserted at this early morning hour.

Juve remained on the platform with Wulf. As a preliminary to making his arrest, he took out his revolver, and held it in the palm of his hand. Suddenly he gave a yell and sprang forward. Ouaouaoua, taking advantage of the engine driver's absence, had entered his compartment and pulled the levers.

In a moment the train was under way. As Juve made a jump on board, Wulf tried to restrain him, and in the scuffle knocked the revolver out of the detective's hand. To the consternation of the train's crew left behind in the station, the train was now gathering speed. Their shouts in turn alarmed the few passengers, who regarded the precipitate entrance of Juve in amazement. Finally a cry from the powerful lungs of Wulf was heard above all the other noises. A name shouted in terror:

"FantÔmas!"

A rush was instantly made to seize the fool or the madman who had started the train, but a revolver shot quickly drove back the passengers and Juve, furious with the imbecile Wulf for having disarmed him, was obliged to take cover with the others.

The train passed through the Station de la TrinitÉ, shot through Saint Lazare without heed to signal and tore along at headlong speed. And then, in a moment, the train was plunged into total darkness and a cry of rage escaped from the Primitive Man. The detective understood in a flash.

The Nord-Sud had had the happy idea of cutting off the power, and Juve noticed that this occurred just as the train had passed the Station de la Concorde and entered the tube beyond. Ah! this time the Primitive Man was in a tight corner. His revolver would be less dangerous in the darkness.

Juve rose carefully, prepared to advance, when a spark was seen, succeeded by a terrific explosion. A shower of matter fell upon the train, shattering the windows and throwing the passengers pell-mell upon each other.

Then ... silence....

The red lights of torches gradually lighted up the tunnel in which the tragic accident, still unaccounted for, had occurred. Juve, unconscious for ten minutes, came to his senses and realized with a sense of relief that he was unhurt, and that the men directing the rescue were the Paris firemen. Many persons had been wounded, but by an apparent miracle not one had been killed.

The Primitive Man had disappeared.

Juve, in quest of clues which might lead to the discovery of the explosion, climbed upon the train to where an immense hole in the roof of the tube had showered down bits of asphalt and broken earth. He noticed quickly that communication had been opened with the Place de la Concorde. By dint of hoisting and scrambling he succeeded at length in gaining the surface of the ground.

Vague groanings came from the mass of stones piled not far away. As he approached these noises, they became more distinct. Finally, he discovered the body of a man wedged between two large blocks and covered with a piece of gas-pipe.

The body was begrimed with soot and mud. Juve, after hauling his burden to the open air, where he was greeted with cheers by the crowd, dipped his handkerchief in the water from the fountain and wiped the man's face. Suddenly, he dropped to his knees with a cry:

"Fandor! It's Fandor!"