Making sure that they had left behind them no evidence of their presence the two airmen re-ascended to their lofty perch.

"You're steaming like an overworked horse, old man," said Billy addressing the A.P. "I'll throw your coat over you. You can't sit up or the Fritzes will spot us."

Trudging across the tilled land were eight or nine greatcoated Huns, armed with rifles. Two of their number were drawing a light cart.

"What's that for, I wonder?" whispered Kirkwood, for the Germans were still a considerable distance off, yet making almost in a straight line for the tree in which the three chums were hidden.

"Can't say," replied Fuller. "I never saw Huns with a contraption like that before. Rations, possibly: they may mean to camp out here just to keep us company."

The fugitives were not left long in doubt, for on arriving at a spot twenty yards from the edge of the wood the party halted and proceeded to don flexible metallic masks with hideous-looking snouts. This done, the corporal in charge inspected each man's face-protection with deliberate thoroughness, while from a distance two Hun officers in the uniform of the Engineers watched the proceedings.

"By smoke!" muttered Barcroft under his breath. "They're going to have a shot at ga.s.sing us."

At a brisk order the lid of the cart was thrown back revealing a couple of cylinders to which were attached lengths of armoured metallic hosepipe terminating in elongated nozzles. First the cylinders were placed upon the ground and air pumped into them until the required pressure was obtained. Then each apparatus was strapped to a man's back, a soldier being in attendance to hold the nozzle.

It was fairly safe for the three British officers to watch the proceedings since the height of the branch enabled them to look down upon the heads of the ga.s.sing party, while the latter could not look up owing to the straps that secured the lower portion of their masks to their shoulders.

"Reminds me of goblins at a panto," thought Bobby. "Wonder when they're going to start?"

As a matter of precaution he tied his handkerchief over his nose and mouth, an example that his companions hastened to copy. They realised that it was but a sorry protection--useless against the full strength of the deadly chlorine, but sufficient, perhaps, to ward off the effects of a "tail-end" of the poison-cloud.

Weirdly fascinated the fugitives watched the proceedings. It seemed strange to witness the diabolical preparations for their intended execution. Dimly Barcroft wondered whether he would be conscious when he fell from the bough, or whether the gas would overcome him instantly.

"The first whiff and I'll shoot," he thought grimly. "I'd like to shatter the nozzles of those pretty masks and let the brutes have a good sniff at their vile mixture."

A faint hiss betokened the fact that the taps controlling the discharge tubes had been turned on. Clouds of black vapour, eddying and seething, issued from the nozzles and rose sullenly in the cold, damp air.

CHAPTER XXIX

Ga.s.sED

SOMETHING fluttered past the flight-sub's ear. It was a dead leaf.

Whisked by a sudden gust it disappeared. Simultaneously the wind moaned dismally betwixt the gaunt branches.

Hitherto the air had been heavy and still. Now, almost miraculously, a stiff breeze had sprung up, blowing in the direction of the infernal gas cylinders, just as they liberated their poisonous contents.

The rolling columns of vapour, forced back by the wind, literally enveloped the hideously masked operators. More, the deadly cloud, keeping close to the ground, travelled at prodigious speed towards the two Hun officers, who hitherto had been thoroughly enjoying the proceedings.

Quickly their brutal hilarity changed to an att.i.tude of terror, as the death-dealing gas, spreading from the right and left of them, bore down at a rate exceeding that of a trotting horse. For a brief moment Barcroft had a vision of two grey-coated forms, two pairs of heels in the air and two pairs of outstretched arms. Then the cloud hid them from sight.

Already the operators, finding that the gas had been misdirected, had shut off the controlling valves. But the mischief was already done. When the cloud had drifted away before the now steady breeze the German officers could be discerned lying on the ground and beating a frantic tattoo with their elbows and heels as the poisonous vapour tore their lungs.

Aghast the corporal watched his superiors' death agonies. While his men hastened to render aid--a useless task--the luckless non com., tearing away his mask and liberating the poisonous vapour, held his face close to the hissing nozzle. Then he, too, dropped, writhing on the ground in mortal pain.

Finding that the gas-masks impeded their action the men who gathered round the dying officers discarded their protection, since the fumes of the first discharge had pa.s.sed far beyond the scene. But they had not reckoned on a repet.i.tion of the dose. Suddenly overwhelmed by the fumes that issued uncontrolled from one of the cylinders, five of the men were stricken down. The remaining few, who had not deprived themselves of their masks, made no attempt to check the outpouring cloud. They promptly fled.

"By Jove, if the wind lulls we are done for!" thought Barcroft. "A fellow wouldn't stand a ghost of a chance after a sniff of that stuff. Wonder how long the gas lasts?"

A back eddy sent a faint tinge of chlorine over the prostrate trio.

It was as much as Billy could do to restrain himself from tearing his handkerchief from his mouth and gasping for breath. Fuller coughed heavily, while the A.P. rose to a kneeling position. Had not Barcroft grasped him by the arm he would have toppled off the bough.

Then came another rush of pure air and the danger was past.

It was nearly twenty minutes before the apparatus exhausted itself.

For nearly half a mile the track of the gas could be followed. The rich dark earth was turned a sickly yellow. Trees on the edge of the adjoining field were literally bleached by the corrosive vapour, while its effect upon the bodies of the victims of their own infernal contrivance was to make it difficult to distinguish between the colour of their uniform and that of their hideously drawn features.

"I vote we shift," suggested Barcroft. "The Boches evidently have a suspicion that we are somewhere in this wood. It's positively not healthy to remain."

"I think otherwise, with due deference to you," objected Fuller.

"Granted the Huns imagine we are here. Those bloodhounds told them that; but after this delightful fiasco of the gas-business they'll take it for certain that if we are here we've been done in. So it would be well to sit tight till dark--much as I want to be on the move."

"What is the effect of chlorine gas upon food?" inquired the A.P.

"Rotten, I should imagine. Why?" asked Billy in surprise.

"Because there's food and drink down there," continued Kirkwood, pointing to the body of the corporal. "These fellows, for some reason, are in heavy marching order. There's almost certain to be grub in his pack and I can see his water bottle. We can't afford to be too squeamish, you know."

"Don't fancy German tack steeped in poison," remarked Fuller.

"Although I feel as if I could eat almost anything. As for water--well, there's plenty of that about."

"And that's what makes me think that the fellow has something better than water in his canteen. At any rate, here goes."

Giving a glance round to see that no one was in sight the A.P. again descended to earth. Gingerly unbuckling the dead soldier's knapsack he produced half a loaf of black bread, a tin of meat and a hermetically-sealed box that afterwards proved to contain biscuits.

One sniff at the bread was enough. Kirkwood promptly replaced it and carefully rebuckled the straps of the pack. The man's water-bottle he risked taking. Uns.c.r.e.w.i.n.g the cork he found that the bottle contained neat Schnapps.

"One teaspoonful only for you, Fuller," he announced as he rejoined his comrades with the spoils. "Raw spirit will play the deuce with that wound of yours."

"You are quite right," agreed the flight-lieutenant as Barcroft proceeded to prise open the meat tin. Its contents consisted of tightly packed sausages. "For the same reason I suppose I must abstain from rich food. Give me a biscuit, you despoiler of the dead."

Late in the afternoon another party of Germans arrived upon the scene, this time merely to collect the victims of the gas and to remove the instruments of retribution.

"Double patrols at all cross-roads to-night, curse it!" said one of the soldiers. "Always more work. These Englishmen must be stiff by this time. Why send us out to arrest corpses?"

"We don't know that the gas has settled them," replied his companion. "Although it did the trick very neatly for Johannes Muller. I'm sorry for him. As for the ober-leutnant----"

He shrugged his shoulders expressively. Evidently the officer was a typical Prussian.

"These English airmen played the deuce at Aerschot and Lierre,"

continued the first speaker. "It will go badly with them if they're caught, but, as I said, it's my opinion that they are done for already. Double patrols on a night like this. It's as bad as the trenches at Ypres."

"Fortunately I am warned for the Golden Lion cross-roads," said his companion. "As soon as the leutnant has made the rounds our party will make tracks for the cabaret. I am an old campaigner, Fritz."

"Ach! Do not, then, get caught," cautioned the other as he slammed the lid of the box on the cart. "It will be safe enough between midnight and two o'clock. I've a mind to join you, only it's a goodish step from Quatre Vents."

"Where's the map?" inquired Fuller, after the fatigue party had disappeared. "The 'Golden Lion' he said? That's it--_le Lion Dor_--it's marked here. Luck, boys! It's on the way to the frontier. Roll on, eleven o'clock. Only six hours more. Why didn't we bring a gramophone, or even a pack of cards?"