in his anxiety to learn the truth dan was perfectly willing to be arrested on whatever charge penn might wish to bring against him. after all, publicity was what he chiefly aimed at, and if he gave his reasons for threatening the secretary, he felt confident that the man would find it difficult to clear his character. certainly halliday had not intended to take penn’s life, and had not the man been such a coward he would have simply laughed at the idea of being tilted out of the machine. but his nerves, shaken by the possible danger, had given way, and he had said much which he would have preferred to keep locked up in his heart. but that the aeroplane, by dipping so low, had afforded penn the chance of escape at the risk of a rough fall, he would have spoken at greater length. and yet, after turning the matter over in his own mind, dan could not be sure of this.

but this much halliday had learned. a gang assuredly existed, and the perfume was a sign of recognition amongst the members, who apparently followed each other’s trails by scent. penn declined to say if his late employer had been done to death by the fraternity, but the perfume on the dead man’s clothes answered this question very positively. also the secretary had denied that the false mrs. brown belonged to the gang, a statement which was absurd, as undoubtedly she was the emissary employed to bring about the death. finally, the fact that mrs. jarsell used the sumatra scent brought her into connection with the hampstead crime whatever penn might say. for these reasons dan felt that he had struck a trail, which would end in the capture of moon’s assassin and the breaking up of a dangerous organisation.

on reflection he concluded that penn would have said very little more, even though face to face with what he believed to be imminent death. he had hinted sufficiently to show that revelation was dangerous not only to himself but to halliday, for if the gang learned that their secret was betrayed, it was certain that death would be portioned out to the man who heard, as well as to the man who spoke. on this assumption dan felt confident that penn would take no action in the matter, and would probably hold his tongue about the adventure. if he told any of the gang to which he presumably belonged, he would have to admit that he had betrayed the secret of the perfume, in which case he would assuredly be killed by his unscrupulous associates. the death of dan, as the young man believed, would follow, but he also believed that by taking care of his own skin penn would remove any risk of vengeance following himself; therefore he was not surprised when he heard nothing from penn, or of penn during the days that passed before the morning of the great race. meanwhile he detailed the conversation to laurance.

that young gentleman had returned to town with some regret since mildred vincent was not by his side. but to assure himself of an early marriage by securing a steady income, he flung himself into journalistic work with redoubled energy, working night and day to gain an increased salary. he was in his office employed on a political article when dan presented himself, and was not overpleased to give up even a moment of his precious time. in fact, he grumbled.

“i wish you would come after business hours, halliday,” he said, testily.

“oh, fudge!” retorted dan, lightly. “a journalist hasn’t any business hours. like a king, he is always in harness. why do you require me to tell you such elementary truths, freddy?”

“i have an important article to write.”

“well, then, you can write it in ten minutes or so. i shan’t keep you long.”

laurance pushed away his writing paper, leaned back in his chair, and reached for a cigarette. “what is it, then?” he asked resignedly.

dan paced the office and related his adventure. “so you see, old son, that the perfume is of great importance, as i always suspected.”

laurance nodded gravely. “it appears so. but if what you think is true, would the man have disclosed a secret dangerous to his own safety?”

“people will disclose anything when on the rack,” replied dan with a shrug, “and the aeroplane was my rack. the fool really believed that i would tilt him overboard, and therefore said what he did say to save his confounded skin. if he had not escaped so cleverly he would have admitted more.”

“i doubt it. from the hint he gave, if it was death for him not to confess to you, because you could kill him, it was equally death for him to speak, if his associates are prepared to murder him for babbling. however, we are now quite certain that the gang alluded to by sir charles does exist. undoubtedly he was got out of the way since he knew too much.”

“it is a pity he did not reveal his knowledge to durwin.”

“he intended to do so, but was murdered before durwin arrived, as we know. by the way, durwin is as keen as we are over this search. i met him the other day and he said that he was hunting everywhere for evidence. why not tell him what you have learned, dan? he can make penn speak out.”

“penn won’t speak further,” denied dan abruptly. “i think, as it is, he dreads the vengeance of his comrades.”

“durwin belongs to scotland yard, and has powers to drive penn into a corner, so he may be able to force confession. i think you should consult with durwin about the matter.”

“after the race, then.”

“why not before the race, which does not take place for a couple of days?”

“i don’t like doing things in a hurry,” said halliday, uneasily. “i want to question mrs. jarsell, and see if she knows anything.”

“if she does, which is doubtful, she will assuredly refuse to speak. so far, i see no connection between her and the gang.”

“you forget the perfume.”

“h’m, yes,” said laurance meditatively, “perhaps you are right. i want to have more evidence before i can give an opinion. but since penn told you so much, aren’t you in danger from the gang yourself, dan?”

“i think not. penn, for his own sake, will hold his tongue. at all events he has not moved so far.”

“that doesn’t say he won’t move. i should examine that aeroplane very carefully before the race, if i were you.”

“oh, i’ll do that! i know the machine thoroughly by this time, and if it has been tampered with i shall soon spot the trickery. well, now that i have brought you up to date with my information i shall leave you to work.”

“one moment. is miss moon going to see you start for york?”

“yes. i got a letter from her this morning. she and mrs. bolstreath come to the aviation ground with lord curberry, confound him!” and frowning angrily, dan took his leave. he was anything but amiably disposed towards his rival.

everything was quiet as regards the criminal business for the next two days, since penn made no attempt to punish dan for the fright he had given him. halliday himself was much too eager over the race to trouble about the matter, but he kept a sharp eye on the vincent machine, still stored at blackheath, so as to guard against any tampering. the start was to take place at blackheath, and on the appointed day five competitors were on the spot surrounded by a large crowd of curious people anxious to witness the conquest of the air. amongst those present was durwin, who pushed his way to where dan was looking over his aeroplane. the aviator did not see the lean, keen-eyed man until he was touched on the elbow.

“is it all right, halliday?” asked durwin, nodding towards the machine.

“perfect. she’s a beauty, and it won’t be her fault if i don’t lift york minster before sunset. what are you doing here, mr. durwin? i didn’t know that you took an interest in aviation.”

“i take an interest in this search for moon’s assassin,” said durwin, drily, but in low tones. “laurance saw me and related your discovery. i am looking about for marcus penn and intend to ask him questions.”

“he may be on the ground,” said dan, glancing around, “since lord curberry’s place is a stone-throw away. but he won’t speak.”

“i’ll make him speak,” said durwin with a grim look. “well, i hope you’ll win, halliday. when you return to town look me up. i may have something to tell you,” and he moved away with a significant look.

dan could not leave his machine, or he would have followed, as there were several questions which he greatly desired to ask. the day was cold and dry, with few clouds, and a good deal of sunshine, so the conditions for the race were fairly good. the wind was rather high, and that vexed the aviators, as the art of flying is not yet so perfect as to control the winds when they are over-strong. however, to go against these powerful air-currents would be an excellent test of the qualities of the various machines. the start was to take place at one o’clock, and the competitors hoped to reach their destination before five o’clock. some of the aeroplanes could travel at forty miles an hour; others at fifty, but so far as dan knew, his was the sole machine which could gather sixty-miles-an-hour speed. if vincent could be believed, the aeroplane ought to travel the hundred and eighty odd miles, if the conditions were tolerably good, in a trifle over three hours. dan, now having perfect mastery of the biplane, hoped to accomplish the wonderful journey in a shorter space of time. but this hope had yet to be verified.

meanwhile, having seen that all was in order, he turned to speak to lillian who had just come up accompanied by mrs. bolstreath. lord curberry was in attendance, and in the distance dan caught a glimpse of the yellow-faced secretary, looking unhappy and nervous.

“oh, dan, i do hope you will win!” cried lillian, who looked extremely pretty, but more than a trifle anxious; “it does seem so dangerous to fly in such a light machine.”

“she’s the best i have yet struck,” dan assured her. “don’t you think she’s as perfect as lillian, mrs. bolstreath?”

the elderly lady laughed and cast a side-glance at curberry, to see how he took halliday’s complimentary speech. “well, i suppose you cannot think of anything prettier to say. i have heard of a woman being compared to a gazelle and to a ship, but never to a flying-machine.”

“mr. halliday is very up to date in his compliments,” said curberry with a slight sneer. he was a tall, bilious-looking man, with pale blue eyes and a thin-lipped sinister mouth, not at all prepossessing in appearance, although immaculate in dress.

dan laughed. being confident that lillian would never marry this spectre, he could afford to laugh. “we young people,” he said, with emphasis, “go with the times, lord curberry.”

“meaning that i belong to the past generation,” retorted the other with a flash in his pale eyes; “you will find that i don’t in some ways,” and he glanced significantly at lillian.

mrs. bolstreath looked nervous, but miss moon was supremely indifferent. she did not care for lord curberry, and in spite of her uncle’s advocacy had not the slightest idea of marrying the man; therefore she ignored him as consistently as she could considering the way he thrust himself into her company. without taking notice of this passage of arms, she began to question her lover about the airship, and gathered quite a stock of information before the start. curberry, being ignorant of aviation, was out of the picture, as the saying goes, so fumed and fretted and looked daggers at dan. it took all mrs. bolstreath’s diplomacy to keep him in a moderately good temper. luckily laurance strolled up, note-book in hand, as he was reporting for “the moment”, and greeted the party gaily. he knew curberry slightly and nodded to him without any word or salutation. in common with many other people, freddy did not like the man, who was by no means a popular character.

“isn’t it a splendid day for the race, miss moon,” said laurance, casting an upward glance at the grey sky. “i look forward to chronicling dan’s triumph in ‘the moment’ tomorrow morning. well, old fellow,” he slapped halliday jovially on the back, “are you prepared for what jules verne would call the very greatest journey of the century?”

“the century is yet young,” replied dan, drily, “and it’s only one hundred and eighty odd miles i have to travel. considering that aviators have reached a successful distance of five hundred miles this race is a trifle.”

“well,” said lord curberry, trying to be amiable — a hard task for him, seeing how much lillian was taken up with the hero of the moment —“aviation has certainly accomplished wonders since santos dumont took his flight of ten yards some four years ago.”

“oh, you do know something about aviation, lord curberry,” said dan coolly.

“i know that it is dangerous, mr. halliday.”

“oh, dan.” lillian grew pale, knowing what the spiteful speech meant.

“i think flying looks more dangerous than it is,” said dan, with a reassuring glance, “and miss moon has come here to be my mascot.”

“you will wire your safe arrival as soon as you get to york,” said mrs. bolstreath anxiously.

“oh, every one will wire,” cried freddy, taking out his field-glass, “the telegraph offices will be kept hard at work all the night. as sure as i stand here, mrs. bolstreath, dan will be the richer tomorrow by ￡2,000.”

“if he is safe, i shall be content,” breathed lillian, and she looked as though she would have kissed dan then and there, in spite of the presence of the crowd and lord curberry.

that unsuccessful suitor scowled, and was about to make one of his acid speeches, when the authorities arranging the race came to declare that all was ready for the start. already the cinematographs were at work taking pictures of the crowd and the machines and their various pilots. policemen drove back the throng to some distance, so that the aeroplanes might have a clear space to run in, and just as the hour of one sounded the start was made amidst a breathless silence. the aeroplanes ran along the ground like startled hens, and sprang into the air at various points. the eyes of the people from looking level now began to stare upward at the diminishing dots which towered and raced for the north. a zig-zag monoplane was leading, but lillian had only eyes for dan’s craft. freddy gave her his field-glasses so that she might get a better view. three of the aeroplanes bunched, but two circled away some distance in wide arcs, and of the two, one machine belonged to dan. the onlookers saw him increase the speed of his propeller and then, like an arrow from the bow, he sped swiftly out of sight in a straight line. a cheer rose from the throng, as the vincent biplane was leading by some lengths, and lillian gave freddy back his glasses.

“i hope he’ll come back safe,” she said, with quivering lip.

“of course he will,” laurance assure her. “dan is one of the most cautious aviators we have.”

“but there is always a risk,” sneered lord curberry.

“probably. only a brave man would take the risk.”

“you don’t fly yourself, mr. laurance.”

“as you see,” was the calm reply, as curberry’s enmity was too paltry to trouble about. “well, miss moon, we can’t see anything more, so i suppose you will go home.”

“miss moon is coming to luncheon with me,” said lord curberry, “and mrs. bolstreath also.”

“i am very hungry,” said that lady pensively, “so i don’t say —”

“hallo!” interrupted laurance, as a clamour arose on the outskirts of the now fast diminishing crowd, “what’s the matter? in the interests of my paper i must see what is taking place,” and with a hasty raising of his hat to the ladies he left them to the care of lord curberry.

as he pushed his way towards the commotion he heard a voice asking if the man was quite dead, and fancied that some one must have fallen down in a fit. but when he broke through the ring of policemen, and beheld durwin lying on the ground, with staring eyes and a ghastly, expressionless face, the sight so startled him that he caught a constable’s arm.

“what’s all this?” he demanded hoarsely. “is mr. durwin dead?”

“durwin,” echoed the policeman sharply, “do you know the gentleman?”

“of course. he is mr. durwin, one of the scotland yard officials. i wonder you don’t know that.”

“i never heard of him, sir. he must belong to the detective department.”

“what’s the matter with him; has he had a fit?”

“he’s been murdered,” said the constable, shortly.

“murdered?” laurance stared at the man in a horrified manner, and his thoughts flew to the gang which he and dan and durwin were trying to root out. was this another crime similar to that committed at hampstead, when sir charles was killed for knowing too much? “is there a fly on him?” asked the reporter hastily, “see if there’s a fly.”

“a fly?” the policeman evidently thought the speaker was crazy. “what has a fly to do with the matter? here’s the inspector, who was sent for some time ago. you had better speak to him, sir.”

laurance did so, and advanced towards the soldierly-looking official who made his appearance. in a low and rapid voice, laurance hastily explained that the prone man was mr. durwin, of scotland yard, and also handed the inspector his own card. meanwhile a doctor was examining the body, and found that the deceased had been murdered by having a dagger thrust under his left shoulder-blade. he was quite dead, and must have passed away almost immediately the blow was delivered. the inspector received this uncompromising statement with natural surprise, and knelt down beside the corpse to verify the declaration. there was no doubt that the medical man spoke the truth, for a stream of blood stained the back of durwin’s coat, and had soaked into the ground. the thrust must have been made with a very sharp instrument, and was undoubtedly delivered with great force.

“who knows anything of this?” demanded the inspector, rising and looking at the awe-struck faces of the crowd sharply.

a slim lady-like girl stepped forward. “i was standing close to the gentleman,” she explained nervously, “and we were all looking at the airships as they went away. i heard him give a gasp, and when i turned at the the sound, he was slipping to the ground. that’s all i know.”

“did you see any one strike him?”

“no, i didn’t. how could i, when with the rest i was staring at the airships going away. the gentleman was staring also, i think. but of course i didn’t take much notice of him, as he was a stranger to me.”

“i saw him fall,” put in a rough man, something like a navvy; “he was crushed up against me in the crowd, and i felt him tumbling. i heard him gurgle, too, and heard this young lady cry out. then i saw him on the ground, and pushed back the folk, saying there was a cove dying. “but i didn’t think it was murder,” ended the man, shuddering.

“nor did i,” chimed in the slim girl. “i fancied it was a fit. i’m sure we were all so crushed up with the lot of people, that i shouldn’t have been surprised if he had taken a fit.”

this was all that could be learned, and the inspector took the names and addresses of the two who had spoken. there were other people who had noted the man on the ground, but these were the sole ones to see the fall. they had, as it were, almost caught the assassin red-handed. but it was impossible to say who was guilty, for the throng was so dense and every one’s attention had been so earnestly fixed skyward on the airships that no one could say who had struck down the unfortunate gentleman. the inspector was much impressed when he learned the identity of the dead man. once or twice he had received official letters from durwin, but he had never set eyes on him until he beheld him dead. but for laurance he would not have known who he was, and therefore questioned that young gentleman closely when the body was carried by four policemen off the ground to the nearest place where it could be placed under shelter.

“and what about this fly?” asked the inspector, having heard of the question from the policeman to whom laurance had spoken.

“don’t you remember the case of sir charles moon?”

“yes. the woman who killed him was never discovered. i remember about the fly, and also i remember the letters written to that newspaper of yours.”

“i wrote the first letter that brought forth the correspondence,” said freddy quickly. “sir charles had some idea that a gang of criminals was in existence, and invited mr. durwin to his house to explain. before mr. durwin arrived sir charles was murdered. since then he had been looking into the matter, and i believe that he also learned too much.”

“you think that this gang you mention had him put out of the way?”

“yes, i do, and that is why i asked if there was a fly on him. it’s the trade-mark of these devils, i fancy.”

“well, there didn’t appear to be any fly on him,” said the inspector, in an uneasy tone. “all the same, i think your idea is right. moon was murdered because he knew too much, and mr. durwin has been got out of the way for the same reason; at least, i think so. however, we shall learn more between this and the inquest. you will attend, mr. laurance?”

“of course. i am only too anxious to find out all i can about this dangerous gang. it must be broken up.”

“the breaking up will be attended with considerable danger,” said the inspector, in a very dry tone. then he noted freddy’s address and let him go.

laurance returned to the office of “the moment” and hastily wrote his description of the start for the london to york race, after which he saw the editor and related what he knew about the death of durwin. permitted to write the article dealing with the subject, laurance gave a concise account, and although he did not say too much, yet hinted very plainly that the death of the scotland yard official was connected indirectly with the murder of sir charles moon. remembering that penn was now lord curberry’s secretary, and that lord curberry’s house was near the aviation ground, freddy wondered if penn had been amidst the crowd. dan could have told him that he had been; but, at present, laurance did not know this. however, he had a shrewd idea that as penn was connected with one murder, he was probably connected with the other. then freddy cursed himself for not having observed if there was any special perfume hanging about the dead man’s clothes. as he did not know the particular smell of the sumatra scent he would not be able to say if it was the one dan had traced to mrs. jarsell, but if there was any scent at all, it was worth while looking into the matter. to repair his negligence he finished writing the article — which was very short — and then started for blackheath to view the corpse again.

as he was leaving the office of the paper a telegram was put into his hand. it proved to be from dan, and had been sent from bedford. “had an accident,” ran the wire, “rudder broke. no bones broken, but shaken by fall. i return this evening to town and will call. — halliday.”

“now i wonder,” murmured laurance, when he read the telegram, “if that machine was tampered with, after all. if so, the gang must be getting scared. first moon, then durwin, now an attempt on dan’s life. by jove, i’ll be the next.” the idea was by no means a pleasant one.