Yvette stared in utter astonishment. This was a new d.i.c.k with a vengeance! All his usual graceful courtesy had dropped from him in the instant; the sheer fighting spirit was on top and d.i.c.k was, for the moment, the officer giving commands to his subordinates. His face was set like granite, and into the keen eyes there came a look Yvette had never seen there before. The cheerful, laughing "pal" had gone; in its place stood the fighting machine, pitiless and efficient.

For an instant the girl was almost on the edge of rebellion; then she turned, and, without a word, took her place in the machine. As she did so, she caught d.i.c.k's eye. For an instant the stern face relaxed; then the iron mask shut down again.

For five minutes, while Yvette put on her leather helmet, d.i.c.k studied the 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 photographed indelibly on his brain.

For three thousand feet the Mohawk shot upward at a speed which left Yvette dizzy and breathless. Then they hung motionless, as d.i.c.k peered anxiously earthward. Were they high enough?

With a smothered exclamation Yvette pointed downward. Far below them a light was circling swiftly, darting hither and thither like a will o'

the wisp. No mail plane would behave like that. d.i.c.k decided that here was his quarry.

Silently the Mohawk came down till it was not more than five hundred feet above its unsuspecting prey, the loud drone of whose engine came clearly on the air. d.i.c.k swung round in a circle, following every movement of the machine below, with a swift precision which Yvette keenly appreciated.

d.i.c.k had made up his mind that the offices above the aeroplane shed probably held the key to the problem they had to solve. He knew he could destroy the machine itself. But that would not be enough if the plans remained intact; a new machine could quickly be built. If he could destroy the plans, on the other hand, there would be at least a lot of delay, which would enable the French agents to perfect their plans for discovering the secret. In all probability, he reasoned, the office would serve as the draughtsmen's workroom, and if this were so, a well-placed bomb might destroy the labour of months.

So he watched and waited, until at length they saw the German aeroplane going home. It came down in a wonderfully steep descent which was enough to tell d.i.c.k that the Germans had indeed made a discovery of great importance, and landed so slowly that d.i.c.k could hardly believe his eyes. But, at least, he saw enough to be sure that the descent was not the vertical drop of his own helicopter. His secret remained his own!

Close beside the shed a couple of hooded airmen alighted. Lights were switched on and they began a careful examination of the machine. Five hundred feet above d.i.c.k watched the figures with interest.

Suddenly the men below stiffened and looked skyward, listening intently.

Evidently they had caught the faint sound of d.i.c.k's propellers.

A glance through his bomb sights showed d.i.c.k that he was in the position he desired. There was now no possible escape for the craft below.

Then one of the men pointed upward. Even in the darkness he had caught a glimpse of the Mohawk.

d.i.c.k's hand shot to the bomb controls and he pulled a trigger. A petrol bomb 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 ma.s.s of flames, fed by the petrol which streamed from its tanks. One of the Germans was caught in the outburst and apparently died almost instantly.

The second man, however, dashed into the office. The Mohawk moved forward a few feet and three more bombs fell in quick succession, right on the roof of the shed. Then, her work done, she rose high into the air and d.i.c.k and Yvette watched the results.

The shed below them was already a furnace. Apparently there must have been some petrol tanks there, for no ordinary building could have burned so furiously. In a few minutes nothing remained but a heap of glowing embers.

d.i.c.k watched keenly for the man who had run into the office, but he never reappeared, and it was evident that, trapped by the flames, he had been unable to get out in time, and had perished. d.i.c.k little suspected at the time how important the fate of that man was to prove.

Then d.i.c.k set the Mohawk at top speed for home. Just as dawn was breaking 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 his laboratory at Spandau. The fire was attributed to an explosion of petrol on the professor's aeroplane which had set light to the office.

Unfortunately, the paper added, all the professor's valuable papers and books had been lost.

The secret of the Zingler aeroplane had perished, and the seven dots were 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 distinguished head of the Royal Society. He sat facing the Prime Minister in the latter's room at 10, Downing Street. Round the long table were grouped the members of the Cabinet. They were men who had lived through stormy and troublous times and had met stories of disaster without flinching.

But, as they admitted afterwards, none of the terrible tidings of past years, when the fortunes of the Empire seemed to be tottering, had affected them to the same extent as the few brief words with which the distinguished savant summed up the long deliberations on which they had been 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 nothing whatever can be done to check or prevent this terrible malady?"

"Nothing, so far as I am aware," was the reply. "As you know the most distinguished men of science in England have been at work on the problem. We had a very full meeting last night, and the unanimous verdict was that the disease was not only absolutely incurable, but that nothing we have tried seems capable of affording even the slightest alleviation. The deaths reported already amount to nearly half a million; though the truth is being carefully concealed from the public in order to allay panic, yet practically every community in which the disease has appeared has been virtually wiped out. Curiously enough it does not seem to be spread by contagion. In spite of the rush of terrified people from districts in which it has appeared, no cases have shown themselves except in towns or villages where the mysterious violet cloud has been observed. That phenomenon has been the precursor of every outbreak."

A month before, in the tiny village of Moorcrest, buried in the recesses of the Chilterns, an unoccupied house had suddenly collapsed with a slight explosion. No one was in the house at the time, and no one was injured. 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, and there was no gas laid on in the village.

But the few villagers who were about at the time spoke of seeing a dense cloud of pale violet vapour pouring from the ruins. On this point all observers were agreed, and they all agreed, too, that the cloud was accompanied by a powerful smell which strongly resembled a combination of 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 sinister significance.

A week later a similar explosion took place in Ancoats, a poor and densely crowded suburb of Manchester. In every respect this incident duplicated the happening at Moorcrest. Naturally, it created something of a sensation, and the papers, recalling the Moorcrest mystery, made the most of it.

During the next fortnight similar explosions, all bearing the same distinguishing features, occurred in various parts of England.

Sometimes there would be three or four in a single day in the same, or closely adjoining, areas. The public became excited. Not a single person was injured, the damage done was apparently trifling, since all the houses destroyed were of the poorest cla.s.s. It looked like the work of a maniac--purposeless and without the slightest trace of a motive.

People spoke of Bolshevists and Communists. But what Bolshevik or Communist, others asked, would waste time and effort to inflict such absurd pinp.r.i.c.ks on Society?

They were soon to be undeceived. An enemy of Society was indeed at work armed with a weapon of a potency which far outstripped the paltry efforts of the Terrorists of old, to whom the bomb and the revolver were the means of world regeneration.

The explosion at Moorcrest took place on May 2nd.

Twelve days later, on May 14th, Doctor Clare-Royden, who was in practice at Little Molton, a village about four miles from Moorcrest, received an urgent message from an old patient summoning him to Moorcrest.

Doctor Royden, jumping on his motor-bicycle, answered the summons at once. A terrible surprise awaited him.

Practically every inhabitant of the village, about a hundred people in all, were in the grip of a fearful and, so far as Doctor Royden's knowledge went, wholly unknown malady.

Its princ.i.p.al symptoms were complete paralysis of the arms which were strained and twisted in a terrible manner, fever which mounted at a furious speed, and agonising pains in the head. Many of the victims were already _in extremis_, several died even while the doctor was examining them, and in the course of a few hours practically everyone attacked by the disease had succ.u.mbed. The only ones to recover were a few children, too young to give any useful information.

It would be useless to trace or describe the excitement which followed, even though the Press, at the instigation of the Government, was silent upon the matter. Help was rushed to Moorcrest, the dead were interred and the living helped in every way. The Ministry of Health sent down its most famous experts to investigate. One and all admitted that they were completely baffled.

On May 21st Ancoats was the scene of an appalling outbreak of the disease. People in the densely packed areas died like flies. But there were some remarkable circ.u.mstances which drew the attention of the trained observers who rushed to the spot to inquire into the phenomenon.

Ancoats had been the scene of the second explosion twelve days before.

It was not long before a health official noticed the coincidence that the outbreaks at Moorcrest and Ancoats occurred exactly twelve days after the explosions in each place.

The coincidence was, of course, remarked upon as somewhat suspicious, but it was not until it was reproduced in the terrible outbreak at Nottingham that suspicion became a practical certainty. It was speedily confirmed by repeated outbreaks in other parts of the country. In each case the mysterious malady broke out exactly twelve days after the appearance of the violet vapour. In all cases the symptoms were precisely alike, and the percentage of deaths was appalling. Neither remedy nor palliative could be devised, and the best medical brains in the country confessed themselves baffled.

By this time there was no room for doubt that the terror was the deliberate work of some human fiend who had won a frightful secret from Nature's great laboratory. But who could it be, and what possible object could he have?

Leading scientific men of all nations poured in to England to help. For it was now recognised that civilisation as a whole was menaced; the fate of England to-day might be the fate of any other nation to-morrow.

France and the United States sent important missions; even Russia and Germany were represented by famous bacteriologists and health experts.

International jealousies and rivalries appeared to be laid aside, and even the secret service, most suspicious of rivals, began for once to co-operate and place at each other's disposal information which might prove useful in tracking down the author of the mysterious pestilence.