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