Flight-Lieutenant Lawless sat on an empty soap-box in a large shed watching his mechanic cleaning the engines of a monoplane which was housed there. The Lieutenant was sucking vigorously at an empty pipe, and, although his face wore an expression of deep melancholy, this was not a case of cause and effect, the gloom was due to his thoughts, not to his ineffectual efforts to draw smoke from an unfilled pipe—and he had plenty of tobacco, anyhow.

Misfortune seemed to have dogged his footsteps ever since his transference from the Navy proper into the Flying Wing. In the first place he had discovered, with feelings of mingled astonishment and humiliation, that he was subject to violent attacks of air-sickness which, so far from wearing off, grew more acute as time went on. That this should happen to a man who had navigated a little cockle-shell of a destroyer in the stormiest weather with never a qualm seemed preposterous. But it was so, and, though the shameful secret was shared only by his mechanic, he was always fearing discovery. Also, because the Fates were against him, he had smashed up two monoplanes, and, with his mechanic, only escaped death by a miracle. As a result of the inquiries following upon these two mishaps Lawless had been severely censured, and his chances of being sent out to the Front remained less hopeful than ever.

No wonder he felt depressed at thought of these things, and fervently wished himself back aboard the old Knat, chasing up and down the North Sea in search of enemy ships.

But his meditations were suddenly interrupted by Mike Cassidy, the mechanic. Mike was fumbling in his pockets, a comical look of bewilderment on his face.

"Th' divil!" he said.

"What?" asked Lawless, suddenly waking up.

"'Twas to meself I wus spaking, yer honour."

"Just calling yourself names, eh?" said the Lieutenant, with a twinkle in his eye.

Mike went on searching his pockets, and at last gave an exclamation of relief. The couple of tiny screws which he had carefully wrapped in a piece of paper and then mislaid had come to light. He took them out, and then threw down the piece of paper, which fluttered to the ground. The Lieutenant idly picked it up, his thoughts far away on those visionary battlefields, and glanced absentmindedly at the print. It was a notice issued by the North British Railway, and read as follows:—

"Five Pounds reward will be paid to anyone giving information leading to the arrest and conviction of the person or persons who on the night of the 4th inst. caused disfiguring paint marks to be made on the railway track and girders of the Forth Bridge."

Lawless was not a Sherlock Holmes, so he did not try to draw inferences or make deductions from the statement he had just read. Still, it puzzled him. Why should any "person or persons" employ their leisure moments in dabbing paint on the girders and track of the Forth Bridge?

Lawless tossed the paper aside, and, for a time at least, forgot all about the notice. It was not till later on that he had occasion to recall it.

"I expect we shall have to go out to-night, Mike, so have everything ready," he said, rising to his feet.

"I will that, yer honour!" answered Mike, turning a hot and beaming face upon his superior.

As he had anticipated, Lawless received orders to set out at eight o'clock that night on a scouting expedition. Although the public was kept in ignorance of the fact, the military authorities were nightly expecting a German attack on Rosyth. Every precaution had been taken to render such an attack abortive, and the entrance to the Forth was guarded by destroyers and submarines. Still, the seemingly impossible sometimes happens in time of war, and there was always a chance that the enemy might creep through the defences by some means or other. Already an apparently harmless merchant steamer had been stopped off Leith, and, upon examination, found to be chock-full of dynamite ready to be fired by time-fuses. No doubt this would have been exploded under the Forth Bridge, with the result that no warships could have entered or left Rosyth till the river mouth had been cleared of the dÉbris.

As an additional precaution, therefore, two or three aeroplanes were sent out nightly to scout along the coast from Fife Ness to St. Abb's Head. The aviators so employed found it a monotonous, unexciting task in which, so it seemed, neither glory nor promotion was to be earned.

And this particular night's scouting proved as tame and uneventful as the rest. Under normal conditions, a night flight above the Firth of Forth as far west as Linlithgow would have afforded a most picturesque spectacle with the lighted towns and cities beneath. But now Edinburgh, Linlithgow, and Dundee, and even the small towns and villages, were practically in darkness, since nearly all the public lights, besides those of the great emporiums and factories, were either unlit or else shielded from observation above. And out at sea only merchant vessels showed lights, those carried by warships, large and small, being masked.

"Even the passenger flights at Hendon were more exciting than this!" growled the Lieutenant to himself as, just before dawn, he steered a homeward course in the direction of the Forth.

He little thought as he uttered his complaint that within twenty-four hours he would have had enough excitement to last him a lifetime.

The machine had reached the Forth and was crossing it just above the bridge, when Mike, who sat immediately behind the Lieutenant, uttered an exclamation:

"Are me eyes desaving me, or have the hivins turned topsy-turvy?"

"What's the matter?" asked Lawless, for the patent wind-screen with which the machine was fitted made conversation possible even when travelling at a high speed.

"Thim stars below us, sorr. Sure now, is it upside down we're flying?"

Lawless looked below, and saw what at first seemed to justify Mike's anxiety as to the position of the heavens. Immediately beneath the machine was a cluster of luminous specks for all the world like distant stars, shining up instead of down upon them. They were certainly not lamps of any sort, and the dull glow they gave out seemed as if it might be the reflection of some distant lights. Yet there was no moon, nor, so far as Lawless could discover, anything which could account for this extraordinary effect of reflected light.

He circled over the bridge two or three times, hoping to discover the cause of this mystery, but without success. While he was doing this a train rumbled across the bridge, and during its passage Lawless noted that the luminous specks disappeared. They were again observable as soon as the train had passed, however, and the Lieutenant concluded from this that they were situated on the railway track itself.

"Deuced queer business!" he muttered.

But there was no time to make further investigations that night, so he continued his flight to Montrose, still pondering over the mystery.

"By the way, Mike," he said, when they had alighted opposite the hangar, "don't say anything about those lights we saw on the bridge. I'm going to investigate the matter myself."

Mike readily promised, and Lawless was strolling away when a thought suddenly struck him.

"By Jove!" he ejaculated aloud. "I believe I've got it!"

His memory had flashed back to the notice he had read, offering a reward in connection with certain paint marks on the Forth Bridge. No doubt the misguided "person or persons" who had daubed the bridge had used luminous paint. This, of course, would explain the phosphorescent glow which had so puzzled him.

The question now was, had it been done merely as a joke or for some specific object? If for a joke, it was difficult to see where the humour came in; if for an object, it was equally difficult to see what purpose it could serve.

"I'll have a closer look at the bridge when I've rested a bit," he told himself.

That afternoon the Lieutenant took a train to Queensferry. He then set out to walk back over the bridge along the railway track. The paint daubs were clearly visible, though not, of course, phosphorescent in the daylight. It struck him as peculiar that these marks had a definite shape, or rather two definite shapes. One took the form of a St. Andrew's Cross, the other the form of a star—that is, instead of two intersecting lines of the same length, there were four.

But that was not all. A careful examination showed that these stars were placed at the weakest part of the bridge; in other words the parts which would be easiest to destroy by means of dynamite. Finally, the marks could only be seen from above the bridge, not from below it.

Lawless whistled softly when he had made these discoveries.

He returned to the depot, and went at once to his commanding officer and told him of the discoveries he had made. He also explained at some length his own theory concerning them. The commanding officer listened patiently at first because he was a good-natured fellow and liked to see his officers exercise initiative and resource. But his interest in the story soon flagged, and when Lawless began to state his deductions it wilted entirely. An expression of resigned boredom appeared on the officer's face and remained there till the interview came to an end.

"So you see," concluded the Lieutenant eagerly, "it requires no great effort of imagination to realise what the German plans are."

But it required more imagination than the commanding officer was capable of exercising. Indeed, he was not an imaginative man and prided himself upon the fact. He didn't regard imagination as consistent with the duties of a soldier; consequently, he made no effort to encourage it in those under his command.

"It's a very ingenious theory, very!" he said; "but unfortunately the grounds upon which you base it appear to me to be entirely unsatisfactory."

And for the time being that settled the matter so far as the commanding officer was concerned.

That evening, when the Lieutenant arrived at the hangar preparatory to setting out on the nightly scouting expedition, he brought with him a curious looking implement. It consisted of a stout spar about ten feet long, at the end of which was attached a long, curved knife, not unlike a billhook in appearance.

It was not difficult to fix the spar securely to the machine so that the business end protruded about six feet beyond the driver's seat, somewhat after the manner of a steel-pointed ram. This done, and it being time to set off, the machine was taken out of the hangar and a few minutes later Lawless and Mike were high above the flight station.

Lawless now steered straight for the Forth Bridge, as he wanted to find out first of all whether the luminous marks were still visible. Having satisfied himself that they showed up as vividly as ever, he swept round in an easterly direction, making straight for the open sea.

They had just passed above the Bass Rock, when the Lieutenant, who had been gazing expectantly into the darkness ahead, shouted a question to Mike:

"Do you see anything in front of us?"

The Irishman, who possessed remarkably keen eyes, raised himself a little and peered over the Lieutenant's shoulder.

"B the powers, if 'tis not a dirigible, 'tis the ghost av wan!" he exclaimed.

"I thought so," replied Lawless in a tone of grim satisfaction. "And, what's more," he added under his breath, "she's making straight for the Forth."

Both the aeroplane and the airship must have been travelling at a very considerable speed, for even as the Lieutenant spoke the dirigible changed from a blurred outline into a well-defined shape. There was no mistaking her now—a gigantic Zeppelin, armed, no doubt, with bombs and machine guns.

"Now we'll have a chance of testing this little invention of mine," murmured the Lieutenant, almost with a chuckle; and he gave a glance of satisfaction at the weird apparatus attached to the machine.

As a preliminary to the duel the Lieutenant rose in the air, circled above the dirigible, and then swooped down and passed abreast of the car, so close that the crew could be distinctly seen.

"That's the challenge!" he shouted gleefully. "Now for it!"

Making a wide sweep, he steered full-tilt at the airship's tremendous gas vessel in such manner as to rip it up with the hooked knife attached to the spar. That was his sole weapon of offence, and he hoped, by repeated attacks, to destroy completely the gas-bag and thus cause the vessel to sink.

The task was harder, even, than it looked, for the Zeppelin, like all dirigibles, was provided with a number of separate gas compartments, so that a leakage in one would not materially affect the stability of the whole structure, which would only collapse after several gas chambers had been ripped open.

A strange thrill passed through both men as their little machine rushed against the tremendous bulk of the airship, much as a swordfish might attack a whale. Suddenly there was a tearing, ripping sound; the monoplane quivered from nose to tail with the shock of the impact and then passed right across the top of the gas vessel, the knife rending the fabric as it went.

"Well, that's lost them some gas, anyhow," murmured Lawless as he brought the head of the machine round, ready to swoop down a second time.

As they approached again they could hear shouts from the airship, and the next moment a small projectile whistled past them.

"They're using a pneumatic gun," ejaculated the Lieutenant.

Before another shot could reach them, the knife attached to the aeroplane was again tearing its way through the fabric of the balloon, making a tremendous slit right across the upper part of one side. As Lawless brought the machine round once more he saw the airship heel, and judged from this that she must have lost a considerable quantity of gas, several compartments having probably been ripped open.

"Three or four more attacks like the last, and she'll collapse," he said.

He steered as before straight at the swaying bulk of the airship, which, after the first attack, had reduced her speed to about twenty miles an hour. Then, as the knife thrust itself into the gas vessel, there was a sharp, cracking sound. The aeroplane seemed to stop with a terrific jerk, tilting forward to such an extent that both pilot and mechanic were nearly flung from their seats. Then, recovering its balance with equal suddenness, it darted forward and passed the dirigible.

"Saints preserve us!" ejaculated Mike. "Wus it a cyclone or a church staple that struck us, yer honour?"

As a matter of fact the knife had struck one of the aluminium girders which formed the framework of the balloon structure, and snapped off.

"Be ready to take the steering wheel!" shouted Lawless.

He bent forward, and, picking up a long sheath-knife which formed part of the aeroplane's equipment, placed it in the belt of his leather jacket. Then, turning the machine, he wheeled round once more, rose above the dirigible, and then descended until only a few feet separated the aeroplane from the gigantic gas-bag immediately beneath it.

"Take the wheel now!" he cried, and then, to Mike's amazement and horror, stood up and leapt out of the monoplane, alighting on the broad surface of the airship's gas envelope.

Finding himself safe, he drew his knife and started to rip and hack at the skin of the balloon. He had known, before making his perilous leap, that he was courting almost certain death, for, should he succeed in deflating the gas vessel, he himself would share in the disaster which must follow.

Yet he knew that if the dirigible reached the Forth Bridge her crew would be able to drop explosives without serious interruption. There were no anti-aircraft guns in the neighbourhood at that time, while an attempt to beat off the aerial monster with rifle fire would be hopeless. He alone could avert the threatened disaster.

The monoplane, now in charge of Mike, had disappeared in the darkness, and Lawless supposed that the mechanic had gone off to give the alarm.

While the Lieutenant was still hacking away at the balloon fabric, a man's head appeared above the rounded edge of the gas vessel. Lawless did not notice him at first, but when the portion of fabric upon which he was kneeling suddenly grew taut under the climber's weight he looked up.

"The devil!" he muttered.

He gripped his knife tightly and drew back a little. He had an idea that he might be able to spring upon his antagonist before the latter had time to assume the offensive. Just as he was about to do this a second head appeared above the edge of the balloon, but on the opposite side and Lawless realised that his first plan was now hopeless. There was nothing for it but to await the attack. Yet even then he could not restrain a grim smile at the thought of his extraordinary position. There had been many strange combats in many strange places; but surely never before had there been a fight on the top of a huge airship five or six hundred feet above the sea.

Nearer and nearer crept the men, one on each side of the Lieutenant, and the latter braced his muscles for the coming struggle. Then, as if acting upon a given signal, the two Germans simultaneously levelled revolvers at him, at the same time shouting something he could not understand.

To have attempted resistance when covered by two revolvers would simply have been courting a useless death, and so Lawless, guessing what they wanted, threw his knife away and made a sign that he surrendered. After all, he reflected, he might do more as a live prisoner than as a dead hero.

The men crawled up to him, and one, who had the end of a rope round his waist, slipped it off and placed the noose beneath the aviator's shoulders, then, both holding the line, they lowered their prisoner down through a sort of hatch, and eventually he found himself standing upon the deck of the airship.

"Who are you?" asked a voice in excellent English; and, turning, the Lieutenant saw that his questioner was an officer, evidently the commander of the Zeppelin.

"Flight-Lieutenant Lawless. Who are you?"

The officer stared at the Englishman for a moment. Then, without deigning to answer what, under the circumstances, must have seemed an impudent question, he turned to give an order to his men.

The great airship lurched forward, and Lawless knew by the rush of wind that she was travelling at full speed again towards her destination. Meanwhile a couple of men bent a rope round his wrists and ankles and then lashed him to one of the elastic steel girders which encircled the car. Ten minutes later the Lieutenant caught sight of a dull glow in the sky to westward, and knew that they were fast approaching Edinburgh—and the Forth Bridge.

Lawless was at the fore-end of the car, and almost in total darkness, for not only were the lights on deck masked, but the crew worked with electric torches which threw out only momentary gleams of light. Taking advantage of this, he began to work the cord which bound his wrists up and down against the sharp edges of the girder till at last he frayed the rope sufficiently to break it.

This done, to remove the cords from his ankles was but the work of a moment, and then he stood free to act once more. For a time, however, he did not move, but stood as though still fettered, in order not to attract the attention of the crew till he had decided what to do.

All at once everybody on board the dirigible was startled by the sound of guns in the distance, and next moment the sky was illuminated by searchlights which swept the horizon like tremendous phosphorescent antennÆ.

Mike had given the alarm!

Several minutes elapsed before the searchlights found the airship and focused themselves upon it, and then everything on board was illuminated by the dazzling rays. A few seconds later the sound of firing increased, and Lawless guessed that a battery of howitzers was being trained on the dirigible. But as yet the distance was too great for the gunners to get the range, and he knew that, even when they did so, the guns fired at too low an angle to hit an object so high above them.

Thanks to the brilliant illumination of the searchlights, he was able to see everything as though it were broad daylight, and, among other things, he noticed hand grenades placed at various points around the car. They were evidently provided for dropping on small objects or groups of men, where the use of a bomb would be unnecessary and wasteful. In a flash he had determined what to do.

The dirigible was now within a mile of the Forth Bridge and about five hundred feet in the air. If the present speed were maintained, it would be directly over the bridge in less than five minutes. The howitzers had by now been supplemented by small groups of sharpshooters, but with the exception of a few stray bullets which occasionally whistled past the small-arm fire was likely to do as little damage as the heavier guns. It was clear that, unless some unforeseen accident occurred, the airship would accomplish her purpose.

As they drew nearer a fresh burst of firing, this time from the bridge itself, showed that two guns had been dragged on to the railway track to command a better range of the approaching airship. But this attempt, like the rest, was in vain, for the shells flew harmlessly below the car, and, even had they been able to reach it, an ascent of fifty feet or so more would have placed the dirigible but of danger again. Only an anti-aircraft gun, firing at right angles to its base, could hit the terrible war machine above.

All this time Lawless was waiting for his opportunity—and at last it came. Springing forward, he seized one of the hand grenades and flung it with all his strength at the gas-bag above his head, hoping that it would explode and ignite the gas. Unfortunately, it struck a girder below the balloon, but in doing so ignited some of the cordage, which, being creosoted, began to burn furiously.

The commander, realising the danger—for the cordage passed over the gas envelope and must soon ignite it—gave some orders, and while several of the crew climbed up in order to try and put out the burning ropes others rushed upon Lawless.

The latter, however, had managed to seize another grenade, and, holding it high above his head, threatened to hurl it amongst them if they advanced another step. While they stood hesitating, and the commander himself seemed uncertain what to do, there came a wild cry from the men who had climbed into the airship's rigging.

Looking up, the Lieutenant saw that, in spite of all efforts, the ropes were still burning. In a few seconds the fire must spread to the balloon, and that meant annihilation.

The commander sprang to a lever, pulled it, and next moment the dirigible began to descend. He had opened the gas valve in the wild hope that the airship might sink to the water safely before the threatened explosion took place. It was their one chance of escape from a terrible death.

Slowly, very slowly, the monster dirigible descended. Everybody had forgotten Lawless in the horror of the threatened calamity, and all eyes were turned towards the smouldering cords, which occasionally burst into flame in the upward rush of wind caused by the airship's descent.

Would they reach the water before the explosion took place? That was the question each man asked himself.

Cork life-belts were hurriedly served out to the crew, who stood by the rails of the car ready to spring out as soon as the distance rendered it moderately safe. Yet all the time the little wisps of flame rose faster and faster, sometimes disappearing, only to be fanned into life again by the draught of air. Masses of charred and smouldering rope fell on the deck from time to time and were promptly flung overboard.

Nearer and nearer to the water sank the airship, and nearer and nearer to the gas holder reached the flames. Now they were not more than a hundred feet above the water; a few more moments would decide their fate. It was a race between the sinking dirigible and the flames, the odds in favour of the flames.

The firing had ceased for some minutes, for all who saw the airship knew that she was going to her own destruction. Boats approached in readiness to rescue the survivors should there be any, but stood off again when it was seen that a tremendous explosion was imminent.

For some seconds Lawless had been watching a small piece of burning cordage nearer to the gas envelope than the rest, and which, apparently, had not been noticed by the crew. Suddenly it flamed up, and he saw it ignite the fabric of the balloon. With a cry of warning he sprang overboard, but even as he did so there was a blinding flash of light, a terrific explosion, and then—darkness.

When Lawless again opened his eyes it was to find himself on a little bed in what appeared to be a hospital ward. His head, he discovered, was bandaged, and when he attempted to raise himself such an agonising pain shot through his left leg that he fell back gasping.

When he looked up again a nurse was bending over him with a cup in her hand.

"Where am I?" he asked in a dazed voice.

"In hospital," replied the nurse gently. "Drink this," she added, holding the cup to his lips.

The Lieutenant obeyed, though he was all anxiety to hear what had been the ultimate fate of the Zeppelin. When the nurse had withdrawn the cup from his lips he begged her to tell him what had happened.

"The papers say it exploded about fifty feet above the water and that everyone on board except yourself was killed," she answered.

He was left to himself for a little while after that, and then the surgeon came to dress his injuries, which consisted of a broken leg and some burns due to the explosion. Shortly afterwards he received a visit from his commanding officer. The latter was in great fettle at the honour and glory which the heroic action of Lawless had earned for the Montrose corps. If he remembered the interview of the previous day, when he had pooh-poohed the Lieutenant's arguments, he made no reference to it. He was not a man to bear malice.

After he had heard the story of the extraordinary battle in mid-air he rose to go.

"By the way," he said, "you'll be pleased to hear that you have been recommended for the V.C. And, by Jove, I'll say this, you've earned it!"

But it was reserved for Mike Cassidy to bring to the invalid a newspaper containing the official notice that the Victoria Cross had actually been conferred upon Flight-Lieutenant Lawless.

"'Tis meself that's afther wishing ye miny happy returns av the day, sorr," he said.