“Hulloa? Hulloa? Hulloa? Hulloa, Croydon? Brussels calling!” cried Geoffrey Falconer one afternoon over the wireless telephone at the aerodrome just outside Brussels. “It’s Falconer speaking. Changing over.”

“Hulloa, Falconer? Yes,” came a clear voice through the ether. “Changing over.”

“Oh, it’s you, Heddon. Would you please ask Dennis to speak to me if he’s there?” said Falconer.

“Right-o! Stand by, and I’ll try and get him. Switching off.”

Falconer, seated at the operating bench in the small wireless office, the window of which commands an extensive view of the aerodrome, with the city of Brussels in the distance, still retained the head-telephones, and waited.

About five minutes later he heard the strong continuous-wave sent out by Croydon, and a moment later another voice exclaimed:“Hulloa, Brussels? Hulloa, Brussels? Croydon calling. Dennis speaking. Dennis speaking. Over.” Falconer drew over the transmitting switch and then asked Dennis, the pilot, whether he was bringing over the air mail in the morning. Receiving an affirmative reply, Falconer said:

“Do me a favour, old chap, and bring over two or three things for me. You can get them put on passenger train to-night if you’ll telephone to the Works at Chelmsford for them. I want them very urgently to-morrow.” And then he gave descriptions of two air condensers and a double note magnifier and a microphone, adding that the tests he was making at the new wireless station he had just fitted near Dinant, on the Meuse, were satisfactory, but he hoped to still improve them.

Dennis, having written down the list, promised to bring them over by air next day, adding that he would be at Brussels just about one o’clock.

Then Geoffrey rose, handed the telephones to the Belgian operator, and switched off.

He had been nearly two months in Belgium, and had had quite a pleasant time. The Marconi Company were fitting the new aerodrome at Bouvignes, opposite old-world Dinant, with a one-and-a-half kilowatt telegraph and telephone set of exactly the same pattern as the new one they had installed at Croydon. Bouvignes had been adopted as the centre of Belgian civil aviation, air lines having been arranged to perform daily services to Paris, Copenhagen, Berlin, Milan, and other cities; hence it was necessary to be in wireless communication with the aerodromes at those places.

Only three weeks before Mrs. Beverley had brought Sylvia over to see Brussels, as she had never been there, and Geoffrey had for a week acted as their guide and shown them the sights of the pleasant little Belgian capital. Of course, during the greater part of the day he was away at Bouvignes, but he returned to Brussels each evening, and the lovers spent many happy hours together.Now, however, mother and daughter had gone on to Paris, leaving the young engineer to complete his work in preparation for the official tests before the new station was taken over by the Belgian authorities.

So next day about one o’clock Geoffrey returned to the aerodrome outside Brussels, and asked the Belgian wireless operator the whereabouts of the Handley-Page.

“She was over Ghent when I spoke to her five minutes ago. She ought to be in quite shortly,” was the reply in French.

So Geoffrey went outside and strained his eyes to the south-west until he at last saw a speck in the distance which each moment increased, until the giant machine approaching came gradually lower, and after making a turn of the aerodrome, landed gracefully against the wind.

“Hulloa, Falconer!” cried Dennis, a round-faced, boyish-looking fellow, as in his leather suit and helmet he climbed out of the machine. “I’ve got your gear all right.”

They waited for the passengers to land, five of them, and chatted the while. Then from among the sacks of mail from England he pulled out a small wooden box, saying: “I went up to Liverpool Street and got it early this morning.”

The customs officer asked what the box contained, whereupon Falconer, who was known to him, chaffingly said it contained cigars. The good-humoured Belgian only laughed, and shrugging his shoulders chalked it as “passed.”

That afternoon, having an unexpected appointment at the Ministry of Posts and Telegraphs, Geoffrey resolved to remain the night in Brussels. Therefore, he had taken a room at Wiltshire’s Hotel up on the Avenue Louise, rather than at the Grand or the Palace, for in summer, both being down in the city, they are unpleasantly hot. He kept his appointment at five, and then walking back to the hotel, dined, and set out for an evening stroll back down the steep hill into the city, where at one of the little tables set on the pavement before the CafÉ MÉtropole, in the Place de BrouckÈre, he took his cafÉ noir.

Unknown to him, however, a slightly-built, thin-faced young man, who had been watching outside the hotel for nearly two hours, had followed him, and taken a seat unobtrusively near the table Geoffrey had selected, but inside the cafÉ in such a position that he could remain and watch.

There is always light, movement, and gaiety on a summer’s night at that point of the Belgian capital, for along the broad pavement passes a perfect panorama of Belgian life.

Geoffrey had been seated for about a quarter of an hour, and was idly smoking a cigarette when suddenly a tall, well-dressed, rather elderly man who was passing, caught sight of him, halted, and crossing to him, exclaimed in excellent English:

“Well, my dear Monsieur Falconer! Fancy finding you here—in Brussels!”

Geoffrey sprang to his feet, for instantly he recognised in the stranger a Frenchman named Henri Amelot, a radio-engineer like himself, who was attached to the powerful wireless station at Croix d’Hins, near Bordeaux, which the Americans erected during the war for direct wireless communication between the American army and Washington, and which had now been taken over by the French Government.

He had met Amelot at Bordeaux about three months before, and he had been of considerable service to him, hence their meeting was a most cordial one, and they sat together for a long time, until darkness fell and the great arc lamps shone above them. And all the time the silent watcher sat idling over the Independance, but glancing at the pair furtively ever and anon.

Amelot told Geoffrey that he was in Brussels in connection with some newly-invented apparatus which they were about to test at Croix d’Hins, while the young Englishman explained the object of his visit to Belgium.“Then your new Marconi set at Croydon gives wonderful results,” Amelot was saying. “Your Air Ministry ought to be greatly pleased with it. I was listening to it at Le Bourget the other day. Speech was marvellously clear.”

“Yes,” replied Geoffrey. “It is an exactly similar set that we are fitting at Bouvignes. My only regret is that Monsieur Marvaut, the Director of Civil Aviation, is absent from Brussels. He’s been away all the time I’ve been here, and there’s no sign of his returning yet—so his lady secretary, Mademoiselle Levie, tells me.”

“Marvaut was in Paris,” said the French radio-engineer. “I saw him about a month ago. He went afterwards to Marseilles. But you mentioned his lady secretary. I did not know he had one. His secretary, Charles Roosen, is with him.”

“But Mademoiselle Odille Levie called upon me on the first day of my arrival in Brussels, and conveyed Monsieur Marvaut’s regrets at his absence,” said Geoffrey.

“Ah!” remarked Amelot. “Then I suppose she is another secretary.” And the subject dropped. Later, Falconer walked with his friend to his hotel, the Palace, and then continued his way alone up the boulevard to the Avenue Lousie, being followed by the silent watcher who had sat so patiently in the cafÉ reading the Independance Belge.

Next morning at ten o’clock a waiter brought to Geoffrey the card of Mademoiselle Levie, and on entering the lounge a pretty, dark-haired, extremely chic young lady rose and greeted him merrily.

“I heard from Dinant that you were here, M’sieur Falconer,” the girl said. “Last night I had a message from Monsieur le Directeur to say that he is returning to his country chÂteau on Tuesday next, and asking whether you could make it convenient to visit him on that evening. He is rather unwell, it seems, and his doctor has forbidden him to come to the Ministry at present.”

“Where is his chÂteau?” asked Geoffrey.“The ChÂteau de Rochehaut, in the Semois, not very far from Dinant,” the girl replied. “He has asked me to get his official car from the Ministry and take you there.”

“It is very kind of Monsieur Marvaut,” Falconer said. “Please tell him I shall be delighted to visit him. I hope the wireless station will be ready for the official tests by Wednesday.”

“Very well,” she said. “I have the car outside now. If you are returning to Dinant I can take you as far as Namur—for I am going there. The morning is delightful.”

Nothing loth, Geoffrey quickly packed his suit-case, paid his bill, and putting into the car the box of instruments which had come over from London by air, got in beside his extremely handsome companion.

But the driver of the car, a smart chauffeur, though Falconer was ignorant of the fact, was the same man who had so closely watched his movements at the CafÉ MÉtropole on the previous night. The morning was indeed glorious, and the run out to Etterbeek, and through the beautiful forest of Soignes to Groenendael, and on by way of Ottignies and Gembloux to Namur, thirty miles distant from Brussels, was most enjoyable.

Mademoiselle, bright and vivacious, was in excellent mood. Several times she had come from Brussels with messages from the director, and called upon him at the TÊte d’Or Hotel, in Dinant, where he had taken up his quarters. Yet more than once it had struck Geoffrey as curious that the messages had always been verbal ones. And now it seemed strange that the invitation to visit Monsieur Marvaut had come through her, and not in the form of a personal letter.

As they were speeding along into Namur, Mademoiselle suddenly turned, saying:

“I expect you may have to wait for a train to take you on to Dinant. I have plenty of time—so I’ll take you on to your destination.”

Hence he asked her to lunch at the TÊte d’Or on their arrival, and they took their meal at a little table out on the veranda which overlooks the rock-girt river, a corner well shaded, where, seated opposite to each other, they both chatted and laughed merrily.

“I saw you one night about three weeks ago at the Opera, in Brussels, M’sieur Falconer,” the girl exclaimed, laughing. “You were in a box with two ladies, one was elderly, and the other was probably her daughter—eh? You seemed very attentive to them—especially to the younger one.”

Geoffrey smiled mysteriously.

“Well—I did not know that you were watching, mademoiselle,” he said laughing. “They were friends of mine.”

“Your fiancÉe—eh?”

“How absurd!” he exclaimed. “Whatever makes you think that?”

“Oh!—well—from your careful attention to her,” said mademoiselle, raising her wine-glass. “When a man is engaged he always has it written across his back. Women can conceal their love, but a man seldom.”

“Just as, I suppose, women delight in tears—eh?”

“Ah! don’t let us be too philosophical. The weather is too good. Let’s keep that for a dark and rainy day,” she laughed, leaving her companion surprised and puzzled that she should have been watching him on that night when he took Mrs. Beverley and her daughter to the ThÉÂtre de la Monnaie.

From the first this very smart girl had puzzled him. In the midst of his work over at the aerodrome on the opposite side of the river she had come to him once or twice with messages of unimportance.

Suddenly, as they sat together over their dessert and liqueurs, Geoffrey recollected Amelot’s words, and asked:

“Where is Monsieur Roosen?”

“Roosen?” she echoed in rather a blank voice, gazing at her companion across the table. He noticed that her countenance changed. But it was only for a moment. “Oh! you mean the—the other secretary who always travels with Monsieur le Directeur. Ah! I do not know, m’sieur. He is away.”

Her confused attitude when he had unexpectedly mentioned Roosen’s name struck him as distinctly curious. Mademoiselle Odille was very charming, it was true, but she was somewhat of an enigma.

Presently she put on her gloves, and rose.

“Thank you, monsieur, for a very excellent dÉjeuner,” she said. “And now I must leave you to your wires and bewildering apparatus, and get back to Namur and on to Brussels.”

“You must come and see the official tests on Wednesday, mademoiselle. No doubt you will like to hear the wireless telephone,” he said.

“I shall. I’m intensely interested,” she declared. “But remember on Tuesday I will meet you here at about seven and take you over to the ChÂteau de Rochehaut.”

And she got into the car and drove away.

Geoffrey telephoned over to the aerodrome to send the service car over for the box of apparatus, and when it arrived, he drove across the river and through the ancient village of Bouvignes. The old place, surmounted by the ancient ruins of CrÊve Coeur, the castle where the Three Ladies of CrÊve Coeur, sole survivors of the garrison besieged by the Duc de Nevers in 1554, hurled themselves from the tower to death in the eyes of their French conquerors, was quiet and out of the world. But Geoffrey was much preoccupied as the car tore through the dusty village and away up to the plain, where the great new aviation ground was being constructed.

On one side stood the row of up-to-date hangars, with all the latest inventions of British and French aviation, while on the other, facing it, rose the aerial wires on eighty-feet poles temporarily erected, for the lattice masts were in process of manufacture.

In two long army huts, situated a short distance from each other, the wireless office had been established. One of them housed the generator and transmitting gear, while in the other was the operating key and reception set. To the latter hut Geoffrey went, and there, with the assistance of a Belgian wireless operator, he unpacked the double-note magnifier and condensers which had travelled by air from Croydon.

Then throughout the remainder of the afternoon the keen young engineer was engaged in setting them up upon the operating bench. With many patient tests he listened-in constantly for various stations of between nine hundred and sixteen hundred mÈtres. The small oblong box, on the ebonite top of which were fixed two little vacuum tubes which shone brightly when current was passed through them—the piece of apparatus used in conjunction with the seven-valve amplifier—magnified the weakest signal to such an extent that the telephones could hardly be borne upon his ears.

He had another there, but it somehow did not give such good results as the one he had just requisitioned from Chelmsford. As a matter of fact, it was one of a rather newer design, for wireless apparatus is every week improving. And so rapid is the advance of radio discoveries that much of the latest experimental apparatus to-day will six months hence be relegated to the scrap-heap.

Through the whole afternoon he worked on patiently, joining up the receiving circuit of many wires, the transmission side being already in running order. Only three days before he had spoken over the radio-telephone to Croydon, Lympe, Pulham in Norfolk, Le Bourget, and Cologne. Each test gave excellent results, even though the atmospheric conditions were none too good.

So he had every hope of the official tests being satisfactory. As a loyal and trusted servant of that wonderful organisation, the Marconi Company, he had worked hard and done his level utmost to make the Bouvignes station a credit to his employers. Hence he was most anxious that on the great day when the final tests were made everything should go right, and that signals by continuous-wave telegraphy, direction-finding, and radio-telephony should be equally satisfactory.

He was listening to Paris transmitting to Bucharest, reading the commercial messages, and gazing through the small window of the Army hut away across the grass-covered aerodrome to where, below, the winding Meuse lay bathed in the soft evening light. Still listening, he raised his wave-length until he heard the peculiar arc note of N.S.S.—which is Annapolis in the United States—sending its time signals, for it wanted a minute to five o’clock. Having compared the time with the big round clock above the bench he reduced his wave-length to one thousand mÈtres, when suddenly he heard the shrill high-pitched note of a continuous-wave transmitter which sounded as though it were in the near vicinity.

It was calling S.R.4. repeatedly, without giving its own call-sign. But as the wireless station being called did not appear in the official register at his elbow, he took it to be some private station and disregarded it.

At that moment Captain Hanateau, who was in charge of the new aerodrome, entered the hut, saying in good English:

“Here is a telegram for you, Meester Falconer.”

Geoffrey thanked him, tore open the message, but as he read it, he held his breath in anxiety and astonishment. His heart stood still.

It was from Mrs. Beverley, dated from the Grand Hotel, in Paris, asking whether Sylvia was with him. Four days before she had suddenly packed a small dressing-case during her mother’s absence, and left the hotel, leaving behind a note stating that in consequence of an urgent telegram from Geoffrey she had gone back to Brussels and would write.

Geoffrey had sent no telegram! What could have happened?

The Captain saw that the news distressed the young radio-engineer, and expressed his regret if the message was disconcerting.“Yes, it is,” replied the young man as he removed the telephones from his ears and re-read the long message. “Is the car in use? I must go to Brussels at once.”

“You can have it, of course. I’ll go and order it for you.”

Therefore, a quarter of an hour later Geoffrey was speeding back over the dusty road to Brussels. On arrival his first inquiry was at the Palace Hotel, where Sylvia had stayed with her mother. Nobody, however, had seen her there since her departure for Paris. He drove up the boulevard to Wiltshire’s, and there made similar inquiry, but to no purpose. To other places he went that night, making diligent inquiry everywhere, and then he drove out to the aerodrome, for she had been with him there once or twice. But no trace could he discover of her.

So at eleven o’clock he sent a telegram to her mother saying that he had not seen her, and that apparently she had not come to Brussels. He added that he had sent her no telegram.

Sylvia, to whom he was so devoted, was missing! But why?

Just before midnight, so perturbed had he become, that he went to the Bureau of Police, and there saw Monsieur Guiette, the well-known Belgian chef de la SÛretÉ. To him he told the story, after explaining who he was. The official heard him patiently, and promised to have some inquiries made. He suggested, however, that inquiries should be also made in Paris, as perhaps the young lady had not left for Brussels after all.

“She may have gone to London with some motive known only to herself,” Monsieur Guiette suggested.

“But the telegram which purported to have been sent by me must have been despatched from Brussels,” urged Falconer.

“Agreed, monsieur, but that telegram does not appear to have been seen. The young lady herself says that she received a message from you. She evidently did not leave it for her mother to see.”

At two o’clock next morning Geoffrey was in the express for Paris, where he arrived at breakfast time, and in frantic haste sought Mrs. Beverley.

“I can’t think what can have happened,” she said in great distress. “The other morning I went out to Armenonville with my friend, Mrs. Bridges, but Sylvia could not come, as she had an appointment at her dressmaker, Martin’s, in the Rue de la Paix. When we returned at one o’clock we found that she had gone, leaving this note.”

Geoffrey read the scribbled note of his well-beloved, which explained how soon after her mother had gone she received a wire from him urging her to come to Brussels at once, as he was in a great difficulty, so she had caught the next train.

Falconer stood staggered. He had sent no telegram, and he certainly was in no difficulty.

“It is curious that she did not leave the telegram for you to see,” remarked the young radio-engineer.

“She forgot it, I suppose,” replied the mother.

“True, but it may be that she did not go to Brussels at all! The police will probably assist us, though they are never very anxious to help when people leave home of their own accord.”

“Oh, do go and see them, Geoffrey. Do go!” Mrs. Beverley implored, for she was in a terribly agitated state of mind. She had inquired of the servants at Upper Brook Street, but they had seen nothing of Miss Sylvia.

Geoffrey, spurred to activity by his deep affection for the girl, took a taxi at once to the Prefecture of Police, and a detective was detailed to go with him to the Gare du Nord and there prosecute inquiries. From the stationmaster they learnt that the person who had booked passengers by the Brussels express on the morning of Sylvia’s departure was a certain Mademoiselle Le Grelle. She was also on duty at the booking-office at that moment; therefore, they at once sought her, and the detective closely questioned her as to whether the young English lady, whom Geoffrey described, had taken a ticket for Brussels on the morning in question.

Mademoiselle reflected for a few moments, and then said:

“Yes, I recollect quite well. A young English lady asked me the quickest route to Brussels. I told her that the quickest was by Maubeuge, but the direct, without change, was by Amiens and Valenciennes. She chose the later route. The lady I mean wore a long pale-grey cloak and a small hat trimmed with blue. She was the only girl from Paris by that train.”

“It was Sylvia!” gasped Falconer. “She has a grey cloak. Then she did go to Brussels—after all!”

“Apparently, m’sieur,” remarked the detective. “It is certainly for the Brussels police to inquire at once whether she arrived there.”

Back at the Grand Hotel he related to Mrs. Beverley Mademoiselle Le Grelle’s statement, her description of her dress, and the small dressing-case she carried.

“Well, Geoffrey,” exclaimed the anxious widow “I’m at my wits’ ends to know what to do, or how to act. My girl has disappeared. Surely she had no secret appointment with anybody?”

“I feel certain she had not,” declared Falconer. “There’s some deep plotting at work somewhere. Of that I’m absolutely convinced. But we now have the first clue to her, and we must follow it up without a moment’s delay.”

“Yes, I agree,” said Mrs. Beverley, standing at the window of her private sitting-room, which looked out upon the busy boulevard. “We at least know that she actually left for Brussels. And if she did—then she went there to meet you.”

“But I sent her no urgent telegram! I wrote to her about a week ago saying that I expected to be back home in ten days—after the official tests were through.”

It was then about one o’clock, so Falconer ate a hurried lunch with Sylvia’s mother down in the big restaurant, and at three o’clock returned to Brussels. He was not a man to allow the grass to grow under his feet, for again before eleven o’clock—while Mrs. Beverley elected to wait for news of her daughter in Paris—he was closeted once more with the famous detective, Monsieur Guiette.

The astute, bald-headed little man heard him through, nodding ever and anon, until at last, he exclaimed:

“Bien! M’sieur Falconer. I will have every inquiry made to-morrow, and will send you word to—where?”

Geoffrey hesitated. He was in the midst of the serious wireless tests, and had arranged with other stations to listen-in for his speech.

“Oh, it will be best to telephone to me at the TÊte d’Or at Dinant, or to the new aerodrome at Bouvignes,” he said.

And then he took his hat, and departing, ascended the hill to the Avenue Louise, where he spent a sleepless night at the hotel.

Sylvia, his beloved Sylvia, was missing! Had she fallen victim to some evil and cleverly conceived plot? In the dark hours of the night he became seized by all sorts of terrible apprehensions. That false telegram sent from Belgium showed a distinct malice aforethought, She had, without doubt, fallen into the hands of enemies.

But where?

Unable to sleep, he rose, opened the window, and gazed forth upon the well-lit leafy avenue, so gay and brilliant by day, but now entirely silent save for the soft rustling of the leaves. It was three o’clock in the morning, and he had travelled many miles to and fro to France since last he had slept.

Sylvia’s disappearance was a mystery, deep and inscrutable.

Without some strong motive, such as the receipt of the telegram of distress, she would certainly never have left her mother and travelled so hastily back to Brussels.

For over an hour he sat at the open window trying to solve the problem, and hoping that Monsieur Guiette’s inquiries would have some result. She would certainly have to show her passport at the frontier, where a register would be kept.

Day broke, but he did not return to bed. At five he dressed, and then, after his coffee, he strolled anxiously down the Montagne de la Cour in the morning sunshine towards the Bourse, waiting for midday, when he had arranged to call again at the Prefecture, and hear the result of the inquiries at the frontier.

Noon came at last, and he again sat in Monsieur Guiette’s dull drab room.

“Well, m’sieur,” exclaimed the bald-headed little official, “it seems that mademoiselle, the South AmÉricaine, left Paris as you allege, travelled by the train you mention, and showed her passport at the frontier. She told the passport officer that she was going to the Palace Hotel here, but evidently on arrival changed her mind. Then,” he added, “she was noted by the police at the barrier when she arrived, and was seen to be met by somebody—a woman.”

“Met by a woman?”

“Yes. Here our information becomes a little hazy,” replied the great detective. “One witness says that the woman outside the barrier rushed up to her and gave her some message, while another witness, the collector of tickets, declares that it was a little old man who speaks English, and sometimes acts as guide, who met her.”

“But what happened then?” exclaimed Geoffrey bewildered.

“Both persons tell the same story, that a car was in waiting, and that the young lady entered it very hurriedly, apparently much upset at what had been told her, and was driven away.”

“Driven away into the unknown—eh?”

“Exactly, m’sieur.”

“And how shall we now follow her?”

Monsieur Guiette raised his shoulders, and after a moment’s silence, answered:“The young lady has simply disappeared. We have had in the years of my service, both before the war and since, a number of such cases of English and American ladies being lost in Belgium. But such cases are always difficult to deal with. Girls have lovers—secret lovers—so very often. And when at last traced they are always highly indignant—and never tell us the truth. Ah! m’sieur, when one deals with love one is always mystified.”

“But in the present case I am convinced that Miss Beverley has fallen victim to some plot. She received a telegram purporting to have come from myself, whereas I sent her no message. She obeyed my wish, and on arrival here was given a false message, to which she instantly responded.”

“Yes, m’sieur; I quite agree. But we cannot go further. How can we?” asked the famous commissary.

“I certainly think we ought to. A lady has been enticed to Brussels by a false telegram, and it is the duty of the police to follow up the clue which I have supplied!” exclaimed Geoffrey in indignation at the apparent reluctance of Guiette to carry the inquiry further.

“Please, do not be distressed,” said the famous detective pleasantly. “I have already given orders that the inquiries are to be pushed forward in every quarter. The case interests me personally. And,” he added, “I entirely agree with you. There is some very deep-laid plot, otherwise that urgent telegram would never have been forged.”

Geoffrey was now torn between love and duty. From the Prefecture he at once walked to the Place de la Monnaie, and from the central telegraph office despatched a long message to the missing girl’s mother. He urged her to wait in patience, as Sylvia was known to be in Belgium, and all inquiries were being instituted.

Afterwards he lunched at the Taverne Joseph, close to the Bourse, and later was compelled to take train back to Dinant, leaving the further inquiries in the hands of the Brussels police.

That evening, with faint heart, he returned to the wireless office at the aerodrome and tried to continue his work, tuning up the wireless set ready for the official tests. But it was in vain. He was, very naturally, thinking more of Sylvia than of the elaborate and highly-efficient apparatus under his care, notwithstanding the fact that it represented the latest development of the Marconi Company’s system of instant communication, and was, therefore, of special interest.

Next day was Tuesday. At first he resolved not to keep his appointment with Mademoiselle Levie, who was to take him to see Monsieur Marvaut at his country house on the Semois. Yet Marvaut was the director of the civil aviation, and it was his duty to the Company to see him, if only for an hour. He had told Monsieur Guiette this, and promised to be back in Bouvignes for the test next morning, so that he could be rung up from Brussels.

Torn by stress of apprehension he managed to control himself sufficiently to meet Mademoiselle Odille when about seven o’clock in the evening she drove up before the TÊte d’Or, in Dinant to keep her appointment. The thin-faced watcher was again driving. Meeting Geoffrey she laughed merrily, and asked:

“Could we have a more glorious evening? It has been perfect ever since we left Brussels.”

“Won’t you come in for a moment, mademoiselle?” Falconer asked.

“No, thanks. We’re late now,” she said. “I promised monsieur to get you to the chÂteau before dark. Come, get in.”

So Falconer got in beside her, and a few moments later they were speeding along the narrow, old-world streets of Dinant, past the tall Roche-À-Bayard, a rock in the riverside road, and on through the charming little village of Anseremme. Then by the winding road through beautiful country they went by way of Malvoisin and Monceau, down into the Semois valley, one of the most picturesque spots in southern Belgium, that country now remote and still undisturbed as it was before the Hun invader swept through it with fire and sword on his way to Brussels.

They had left the river and passed through a great dark forest when, in the falling darkness, the young man who drove the car—the same person who had watched Geoffrey in the CafÉ MÉtropole—suddenly turned into a well-kept side road which led to a large country mansion, the ChÂteau de Rochehaut.

The door stood open as they pulled up, and on alighting, mademoiselle conducted him through a large but well-lit entrance-hall, upstairs to a small, well-furnished room on the first floor, where she left him, saying that she would go and fetch Monsieur Marvaut. The heavy curtains of purple silk damask were drawn, and the place presented a more cosy aspect than is usual in Belgian houses.

Suddenly the door reopened and Geoffrey stood amazed, for he met Sylvia face to face!

Both uttered exclamations of intense surprise, and both asked questions at the same moment.

“How came you here, dear?” asked Falconer eagerly. “Why, the police are hunting for you everywhere.”

“I know,” exclaimed a big, thick-set man who had followed the girl into the room, and was grinning evilly. “And the police will never find either of you.”

“Who are you—and what do you mean?” Geoffrey demanded quickly.

“I mean what I say!” was the man’s defiant reply.

“I have met you somewhere before,” remarked Falconer much puzzled, while the girl, who seemed half dead with fright, clung to her lover’s arm.

“Yes,” was the fellow’s response; “we met at the Castle of Zenta, in Hungary, where not only did you escape, but you were the means of sending our brave leader, Franz Haynald, and Koblitz and FranÇoise to prison. I have come from Hungary in order to carry out what has been decided in consequence.”“And what is that, pray?” inquired Falconer.

“We succeeded in bringing your fiancÉe here so that you may both share the same fate—death!” he said in a low, hard voice, his eyes full of the fierce fire of vengeance.

“Stand aside!” shouted Geoffrey. “Let us pass!”

A second later the young engineer found himself cornered with a heavy automatic pistol.

“Move, and I’ll fire!” hissed the man whom he now recognised as a revolutionist named Stadler, who had visited the pseudo-Baron at the great castle in the Carpathians.

Then swift as lightning the fellow slipped out of the door, banged it after him, and ere Geoffrey could reach it, he had bolted it on the outside.

Both realised that they were caught like rats in a trap.

Geoffrey in an instant dashed to the window, only, however, to find to his dismay that it was closely shuttered and barred from the outside. Precautions had been taken to prevent their escape!

“Ah!” cried the fellow from the other side of the door, “let the police search! They will never find either of you now. You see the stove? Go across—and open it.”

They both glanced across the room and noticed a round iron stove about five feet in height, used for burning charcoal in winter.

Falconer crossed, and on opening it, saw within what seemed to be a steel cylinder.

“You’ve seen it—eh?” asked the voice mockingly. “That cylinder contains poison-gas! I will give you two minutes before I turn on your lethal draught—two minutes to wish each other a long farewell,” and the brute laughed heartily in his fiendish triumph.

Sylvia gave vent to a loud piercing shriek when she realised the horrible fate in store for them, and then she fell fainting into her lover’s arms. He bent and pressed his lips to hers for a second. Afterwards he placed her in a chair, and taking up another and heavier chair, began to attack the door furiously, smashing the chair in his efforts.

“The two minutes are up!” cried that mocking voice with a low, exultant laugh. “Good-bye!”

Next second a loud hissing came from the stove as the deadly gas, released suddenly, filled the room. Geoffrey caught a whiff of it, and instantly sank to the ground, inert and unconscious.

When they recovered consciousness they both found themselves in hospital wards, attended by doctors, and both learned later that it was Sylvia’s shriek which saved them.

Monsieur Guiette had fortunately suspected that Sylvia had met with foul play, and wondering whether some mishap might not occur to Geoffrey, had ordered his men to keep strict observation, unknown to the young Englishman, with the result that in the very nick of time they had been able to rescue both of them from that fatal room, and unearth a desperate and widespread plot. They also arrested the dangerous Hungarian revolutionist, Hermann Stadler—who had rented the chÂteau furnished—as well as the young motor driver, and the pretty girl, Stadler’s niece, who had so cleverly posed as the secretary to the Director of Civil Aviation. In a wood at the back of the chÂteau they found in a secluded spot an open grave ready for the reception of the victims!

The wireless tests at Bouvignes were delayed for two days until Falconer recovered, but at them Monsieur Marvaut—who had just returned from France—was present, and all went off most satisfactorily, the results being declared to be greatly to the credit of Geoffrey Falconer.