and, even in hisanxiety, Dick was conscious of an uneasy feeling of irritation at thethought that England was being left so far behind in the race for themastery of the air.
Then he caught sight of the great beams of light that marked theposition of the huge Berlin aerodrome, and a few minutes' flying broughthim above Spandau. He circled twice, looking for Gaston's signals, andat last he dropped lower, caught the gleam of the three lanterns whichGaston had placed to guide him, and brought the machine swiftly downbeside the big barn. Then he leaped from his seat.
He nearly gave a shout of joy that would have aroused every Germanwithin a mile! For there, in the light of the lanterns, stood Yvetteherself.
There was no time for explanation.
"Now's your chance," gasped Jules, wild with excitement, "the Germanplane has just gone up!"
Dick's face hardened instantly.
"Get in, Yvette," he said curtly.
Yvette stared in utter astonishment. This was a new Dick with avengeance! All his usual graceful courtesy had dropped from him in theinstant; the sheer fighting spirit was on top and Dick was, for themoment, the officer giving commands to his subordinates. His face wasset like granite, and into the keen eyes there came a look Yvette hadnever seen there before. The cheerful, laughing "pal" had gone; in itsplace stood the fighting machine, pitiless and efficient.
For an instant the girl was almost on the edge of rebellion; then sheturned, and, without a word, took her place in the machine. As she didso, she caught Dick's eye. For an instant the stern face relaxed; thenthe iron mask shut down again.
For five minutes, while Yvette put on her leather helmet, Dick studiedthe plan which Jules showed to him by the light of a shaded lantern.When the Mohawk jumped into the air every detail of it was photographedindelibly on his brain.
For three thousand feet the Mohawk shot upward at a speed which leftYvette dizzy and breathless. Then they hung motionless, as Dick peeredanxiously earthward. Were they high enough?
With a smothered exclamation Yvette pointed downward. Far below them alight was circling swiftly, darting hither and thither like a will o'the wisp. No mail plane would behave like that. Dick decided that herewas his quarry.
Silently the Mohawk came down till it was not more than five hundredfeet above its unsuspecting prey, the loud drone of whose engine cameclearly on the air. Dick swung round in a circle, following everymovement of the machine below, with a swift precision which Yvettekeenly appreciated.
Dick had made up his mind that the offices above the aeroplane shedprobably held the key to the problem they had to solve. He knew hecould destroy the machine itself. But that would not be enough if theplans remained intact; a new machine could quickly be built. If hecould destroy the plans, on the other hand, there would be at least alot of delay, which would enable the French agents to perfect theirplans for discovering the secret. In all probability, he reasoned, theoffice would serve as the draughtsmen's workroom, and if this were so, awell-placed bomb might destroy the labour of months.
So he watched and waited, until at length they saw the German aeroplanegoing home. It came down in a wonderfully steep descent which wasenough to tell Dick that the Germans had indeed made a discovery ofgreat importance, and landed so slowly that Dick could hardly believehis eyes. But, at least, he saw enough to be sure that the descent wasnot the vertical drop of his own helicopter. His secret remained hisown!
Close beside the shed a couple of hooded airmen alighted. Lights wereswitched on and they began a careful examination of the machine. Fivehundred feet above Dick watched the figures with interest.
Suddenly the men below stiffened and looked skyward, listening intently.Evidently they had caught the faint sound of Dick's propellers.
A glance through his bomb sights showed Dick that he was in the positionhe desired. There was now no possible escape for the craft below.
Then one of the men pointed upward. Even in the darkness he had caughta glimpse of the Mohawk.
Dick's hand shot to the bomb controls and he pulled a trigger. A petrolbomb fell squarely on the German plane and burst with a soft explosion,barely audible.
A sheet of fire followed, and in an instant the German plane was a massof flames, fed by the petrol which streamed from its tanks. One of theGermans was caught in the outburst and apparently died almost instantly.
The second man, however, dashed into the office. The Mohawk movedforward a few feet and three more bombs fell in quick succession, righton the roof of the shed. Then, her work done, she rose high into theair and Dick and Yvette watched the results.
The shed below them was already a furnace. Apparently there must havebeen some petrol tanks there, for no ordinary building could have burnedso furiously. In a few minutes nothing remained but a heap of glowingembers.
Dick watched keenly for the man who had run into the office, but henever reappeared, and it was evident that, trapped by the flames, he hadbeen unable to get out in time, and had perished. Dick little suspectedat the time how important the fate of that man was to prove.
Then Dick set the Mohawk at top speed for home. Just as dawn wasbreaking Verdun loomed ahead. Yvette was saved.
Two days later the _Berliner Tageblatt_ told how the famous scientist,Professor Zingler, had perished in a fire which had destroyed hislaboratory at Spandau. The fire was attributed to an explosion ofpetrol on the professor's aeroplane which had set light to the office.Unfortunately, the paper added, all the professor's valuable papers andbooks had been lost.
The secret of the Zingler aeroplane had perished, and the seven dotswere never heard again.
CHAPTER FOUR.
THE SORCERER OF SOHO.
"Unless we can solve this terrible mystery in the course of a few weeks,it is hardly too much to say that England is doomed."
The speaker was the white-haired Professor Durward, the distinguishedhead of the Royal Society. He sat facing the Prime Minister in thelatter's room at 10, Downing Street. Round the long table were groupedthe members of the Cabinet. They were men who had lived through stormyand troublous times and had met stories of disaster without flinching.But, as they admitted afterwards, none of the terrible tidings of pastyears, when the fortunes of the Empire seemed to be tottering, hadaffected them to the same extent as the few brief words with which thedistinguished savant summed up the long deliberations on which they hadbeen engaged. They seemed pregnant with the very message of Fate.Almost they could see the writing on the wall.
"But, Professor," asked the Premier, "do you really mean that nothingwhatever can be done to check or prevent this terrible malady?"
"Nothing, so far as I am aware," was the reply. "As you know the mostdistinguished men of science in England have been at work on theproblem. We had a very full meeting last night, and the unanimousverdict was that the disease was not only absolutely incurable, but thatnothing we have tried seems capable of affording even the slightestalleviation. The deaths reported already amount to nearly half amillion; though the truth is being carefully concealed from the publicin order to allay panic, yet practically every community in which thedisease has appeared has been virtually wiped out. Curiously enough itdoes not seem to be spread by contagion. In spite of the rush ofterrified people from districts in which it has appeared, no cases haveshown themselves except in towns or villages where the mysterious violetcloud has been observed. That phenomenon has been the precursor ofevery outbreak."
A month before, in the tiny village of Moorcrest, buried in the recessesof the Chilterns, an unoccupied house had suddenly collapsed with aslight explosion. No one was in the house at the time, and no one wasinjured. As to the cause of the explosion no one could form an idea.Nothing in the nature of the remains of a bomb could be discovered, andthere was no gas laid on in the village.
But the few villagers who were about at the time spoke of seeing a densecloud of pale violet vapour pouring from the ruins. On this point allobservers were agreed, and they all agreed, too, th
at the cloud wasaccompanied by a powerful smell which strongly resembled a combinationof petrol and musk. That was all the evidence that could be collected.No harm seemed to follow and the matter was speedily forgotten.
Very soon, however, the incident took on a new and sinistersignificance.
A week later a similar explosion took place in Ancoats, a poor anddensely crowded suburb of Manchester. In every respect this incidentduplicated the happening at Moorcrest. Naturally, it created somethingof a sensation, and the papers, recalling the Moorcrest mystery, madethe most of it.
During the next fortnight similar explosions, all bearing the samedistinguishing features, occurred in various parts of England.Sometimes there would be three or four in a single day in the same, orclosely adjoining, areas. The public became excited. Not a singleperson was injured, the damage done was apparently trifling, since allthe houses destroyed were of the poorest class. It looked like the workof a