CHAPTER I. THE SIGN OF THE THUMB.

“Well, my young skyscrapers, I hear that you were lost in Petrograd, but the special messengers tell me that if anything else was lost it was not time on the way back.”

The aviation chief in Warsaw had this greeting for Our Young Aeroplane Scouts, Billy Barry, U. S. A., and his chum Henri Trouville, when the young airmen completed an interview with Colonel Malinkoff, the officer who had selected them as pilots for the dispatch-bearing aerial trip to the Russian capital.

“Maybe you think we are like bad pennies—always sure to turn up,” laughed Billy. “But, believe me,” continued the boy, “it was no merry jest to us when the strange streets seemed to have no end, and we knew that we were counted upon to pull out by daylight.”

“I can’t figure, upon my life, why you tried to foot it alone; at night, too, in a city like that.”

The aviation chief had another think coming to him, if he imagined for a minute that he was going to hear the real story of the Petrograd adventure from the youths he addressed.

“We thought the walk would do us good.”

Henri had some difficulty in keeping a serious face when Billy offered this plea as an excuse for the performance that had almost brought nervous prostration to Salisky and Marovitch, the dispatch bearers.

In a quiet corner later on, Henri had no desire to even smile when Billy gravely reviewed the possibility of the vengeful Cossack tracing them to Warsaw.

“You know,” said the boy from Bangor, “those fellows hang on like grim death when they have a grudge against anybody, and this wild and woolly scout is evidently anxious to stick his claws into us.”

“Maybe after all,” suggested Henri, “it is just because he thinks we are spies, having seen us working with or, rather, for the other side.”

“Why, then, didn’t he make his spring when we were within easy reach?”

“You forget, Billy,” replied Henri, “that by the time he had patched up his memory we were in Malinkoff palace, and even the tiger of the plains would hesitate before attempting to rough it with a Russian duke.”

“And there was a good reason why he did not have it out with us when we left the palace,” added Billy.

“A backway reason,” concluded Henri.

The Russian secret service, reputed to be a wonderfully efficient system, had now advices of the activities of that eminent arch-schemer, Roque, or whatever other name by which he was known, in this section of the war zone.

The blowing up of the war depot in Warsaw was less a mystery since the authorities had learned of the presence of this dreaded operator even so close as the width of a river.

If the wily Cossack could connect our boys with the previous movements of the aforesaid Roque, then, as Billy would say, “good night.”

In Colonel Malinkoff would be vested their only hope.

That the boys were not crazy about making another journey at present to Petrograd, goes without saying. They would be insane if they did, of their own accord.

But, luckily, their next flying assignment was the piloting of scouts sent out daily to observe the maneuvers of the great army in gray, then working on a new tack to break into the coveted city of Warsaw.

The aviators operated near a battle front nearly forty miles wide, and above a veritable hurricane of gunpowder, but in this experience Billy and Henri had grown old.

Once away from the city, and up in the air, their chief worry was behind them—their Cossack Nemesis could go hang!

From Salisky, now acting as observer in one of the biplanes, the boys learned of the fall of the great underground fortress of Przemysl, in and out of which they had served as aerial messengers, and where they had, not so long ago, bidden farewell to that gallant soldier-aviator, Stanislaws.

“I hope that ‘Stanny’ will be given a soft berth as a prisoner,” said Billy to his chum.

In the presence of the other airmen, however, the boys kept discreetly silent as to their acquaintance with the Austrian fort and town now overrun by the Russian forces.

Now and again there were days when Billy and Henri were relieved of the strain of constant aeroplane driving, and which was given to wandering about the streets of busy Warsaw.

One afternoon their steps inclined to the well remembered square with the tall column and heroic statue of bronze. In the door of a shop bearing the symbol of a silversmith, the proprietor happened to be standing when the boys strolled by.

This tradesman, at the time without trade, suddenly changed from sleepy attitude to one of alert anticipation after second view of the strollers. Under a skull cap of silk gleamed a pair of keen, blue eyes, and the smooth-shaven face of the man was alight with a half-smile of recognition.

He lifted his right hand with a peculiar gesture, the thumb folded into the palm.

Billy, idly glancing at the performer, remarked:

“That fellow wants to sell you a dinner set of fifty pieces, Buddy.”

“That hole in the wall wouldn’t hold half of it,” joked Henri.

The tradesman seemed puzzled at the lack of response to his thumb signal, but he was evidently determined to have a word with the boys.

With a low bow he stepped to the middle of the sidewalk, as if soliciting custom, and in English, with peculiar accent, softly mentioned a familiar term—Two Towers!

Billy started as if a torpedo had exploded underfoot.

“Where have I seen that face before?”

This thought wave was instantly merged into the sense of knowing:—

The coal heaver who had presented the soiled scrap of paper which summoned the young aviators to the twin towers on the day of the destruction of the war depot!

That face, though now clean of grime, was the same that had burned itself into the lad’s memory when the stirring message was delivered.

“I gave you the sign and you did not respond. Why?”

“Blest if I know what you mean,” Billy told the supposed silversmith.

“But it was to you that I was sent when the hour of need was near.”

“Now see here, for good and all, let me say that neither my chum nor myself has any knowledge of the inside workings about which you are trying to talk, and what’s more we don’t want to know anything about them. Mr. Roque showed us a lot, but I guess he stopped somewhere this side of the inner circle.”

Billy did not care to assume any new responsibility which might lead Henri and himself into some maze of mystery far beyond their depth.

The man addressed appeared to be puzzled at the boy’s reference to “Mr. Roque.” He evidently believed that Billy was fencing with him. “Kindly step into the store for a moment; I will not detain you long.”

Though both the boys had reached the same conclusion, that it was a sort of spider and the fly game, they impulsively followed the leader into the little shop.

Spreading a few articles of jewelry and silverware upon the top of the counter, as a cloak for the line of talk he was pursuing, he quickly remarked:

“I sometimes fear that I am a suspect, and we cannot be too careful in these times.”

Billy darted a look at Henri full of apprehension—“we cannot be too careful.”

“It is no use to hide behind the bush, one from the other, my young friends,” continued the man behind the counter; “of course, I do not blame you for being cautious, but now that we are past the limit of assurance, let us get together and talk straight.”

“You still have the advantage of us,” insisted Billy, glancing uneasily toward the door, as if contemplating a hasty move in that direction.

The keen blue eyes under the skull cap flashed a threat of growing irritation.

“Perhaps you do not appreciate, young man,” and the voice of the speaker sounding a harsh note, “that we sink or swim together. It is no ordinary tie that binds us, and woe to the one who breaks it.”

“Say, old scout,” interposed Henri, “this isn’t a theater.”

“Or an asylum,” added Billy.

How the silversmith would have resented these strokes at his manner of dramatic declaration was left for surmise, for at the moment his whole expression changed to one of bland greeting at the sight of a newcomer in the shop—a man who presented a wide front view, wearing a military cape and fairly bristling with authority, evidenced by his manner of pushing open the door and his heavy tread, which raised a creak from the floor as he strode to the counter where the boys were standing.

“They have just dug something that looks like a clock out of the ruins up there, Ricker, and as you are the nearest time tinker around here, I want you to come alone and see what you think of it.”

The boys saw the hue of ashes in the face of the tradesman, but the words that gave him the scare were as Greek to them.

“Certainly, sir; certainly,” the silversmith was saying, as he reached for his hat and greatcoat, hanging on a convenient peg. Turning to the boys, he politely directed them to the door, with an excellent imitation of regret that their expected purchase must be delayed by this emergency call.

On the sidewalk the boys watched the turn of the corner of the burly cape wearer and the silversmith, the latter walking like a weary soldier on a forced march.

“Here’s a pretty howdy-de-do, Buddy,” observed Henri, “getting twisted up with a fellow that evidently has a price on his head, and who thinks we are as deep in the muddle as he is. Did you ever see such luck?”

“If I knew a single word in the outlandish language spoken by that fat policeman I could tell better about our chances of being bothered again by the man with the thumb sign.”

It was not the first time that Billy had been stumped by the various lingoes in the war zone.

While the boys were dreaming that night of lurid initiation into some bloody brotherhood, there came riding into Warsaw a bevy of splendidly mounted horsemen, brilliantly attired in scarlet, gold-braided caftans, white waistcoats and blue trousers—imperial Cossacks from Petrograd!

CHAPTER II. BETWEEN TWO FIRES.

The boys were aroused in the early morning by the shrill neighing of horses in the courtyard underneath the windows of their sleeping quarters, and other sounds indicating the incoming of a cavalry troop, created sufficient inducement, at least, for an after-waking peek at the night-riders who had cut off a good hour of slumber.

Billy, the first at the window, drew back with a sharp note of alarm.

“The fancy Cossacks!” he exclaimed.

“Quit your jollying,” cried Henri, unbelieving, bouncing out of his cot and barefooting it to the lookout point. “Jumping jimminy,” he excitedly admitted, when he saw one of the red horsemen in the act of dismounting, “you are right, sure enough.”

“But what are they doing here?” questioned Billy. “This is no stableyard.”

“Looking for us,” slyly insinuated Henri.

“Maybe there is more truth than poetry in that proposition.”

The boy from Bangor was taking the matter seriously.

In the interval several Cossacks, trailing their lances, crossed the courtyard to the main entrance of the building where the aviators were housed, and vigorously thumped for admission. These knights of the plain evidently held themselves to be privileged characters.

Billy and Henri, getting into their clothes as quickly as possible, poked their heads over the stair railing, from which location they could see and hear all that was happening in the spacious hall below.

By what they heard, however, they were not enlightened, for it was in the speech unknown to them, but enough and plenty in the sight of no other than the Cossack who had given them the evil eye in Petrograd.

The aviation chief seemed to be strenuously saying “no” to some question put by the giant in scarlet, shaking his head and handsweeping over his shoulder in directing manner.

The insistent intruder finally accepted the advices given, and with his companions again took to saddle, spurring their horses into a clattering gallop out of the paved enclosure.

Just as if they had not been watching and listening, the boys descended the stairs, giving their usual good morning salutations to their fellow aviators, who had all been attracted to the hall by the discussion just concluded.

To give the lads an understanding with the rest as to what it had all been about, the chief mingled French and English in his explanation.

“That big fellow is Nikita, who has been attached to the imperial service on account of his skill and daring as a scout. I heard a story about him only the other day. Along with ten comrades, he was captured through falling into an ambuscade. Three days later he turned up at the camp of his command with two bullets, one through his clothes, and one through his thigh. He was horseless, but carried his long lance. Without horse or weapons, he had crept during darkness from the tent in which he slept, got safely past the German sentries, and then reflected that it was a shame for a Cossack to lose his horse and lance. So, as the story goes, he crept back, recovered both horse and lance and galloped away. The horse was killed by a shot from an outpost, but I see that Nikita still has his lance. I tell you that this is a breed that never lets go.”

This last comment had a jarring effect upon both Billy and Henri. The latter, however, did not restrain a desire for some direct information:

“That’s a fine story, lieutenant, but it doesn’t tell what this wonderful warrior wanted here this morning.”

“He demanded an interview with the dispatch bearers who aeroplaned into Petrograd on a certain date—the same date, by the way, upon which you were detailed as pilots for Marovitch and Salisky. I had difficulty in convincing the Cossack that the men he was seeking were at present scouting along the Vistula south of Warsaw.”

“Where I wish we were this very minute.”

Billy had edged close to Henri to say it.

The aviation chief further advised that the Cossacks had gone to the general’s quarters, and would probably remain in Warsaw until they had completed a mission, of which he (the chief) knew nothing about, but which apparently had to do with some recent happening in Petrograd.

Right there the boys made up their minds that they had all the rest they needed, and Billy, as spokesman, so informed the lieutenant.

“If there are any air scouts going out to-day,” said the boy, “we want to be on the job.”

“All right, my birds,” agreed the lieutenant, “you will be marked first on the list.”

When at last the aerial assignment of the boys for the day was made they were greatly interested to learn that the flight was to be directly across the river, in which direction they had never traveled since the day they came into the city by the written directions of Roque.

The observers they were to pilot were immediately identified with the general’s staff, and the young aviators were duly advised of the rank of their passengers.

“They all look alike to me,” remarked Henri, as he and his chum waited at the hangars for the order to start—“all except Colonel Malinkoff, and he’s my pick every time.”

Nevertheless, the pilots showed proper deference when the officers boarded the aircraft, after briefly outlining the plan of journey. The boys did not take the time nor assume the trouble of telling that they needed no guide notes for this particular voyage!

The same old entrenchments skirted the mud-colored river, but thinly populated now, for the main body of German soldiery there had joined in the new move upon Warsaw from the northwest.

Billy and Henri had each an eye for their former earthy lodging, and marked in memory the very spot in the battlefield where the French boy had landed the firebrand Schneider for his desperate dash in rescue of the grounded colors.

Of the fate of the secret agent and his fighting attendant, however, no tidings came up from the mottled plain.

Somebody might know in the clean, white lodge-keeper’s kitchen, where the canary sang, but there was no available excuse to turn downward the swiftly sailing biplanes when they swept over the one bright spot in all that forbidding surface.

“I can recommend your license as master pilots,” jovially observed one of the officers when the machines again rested in the aviation field, just at sunset.

The other observer nodded approval of the compliment to the youngsters, and both found it not beneath their dignity to give Billy and Henri a hearty handshake.

The young aviators had hardly completed the housing of the biplanes when they were accosted by a loutish lad attired in a smock-frock and leather leggins.

With a pull at his forelock, the boy handed Billy a fold of notepaper, and then shuffled away.

“Some more shady business,” muttered Billy, opening the message.

One line, that was all:

“To-morrow noon. Sign of thumb.”

“Why can’t that fellow let us alone?”

With the petulant words Billy tore the note to shreds and cast them to the wind.

“Between the Cossack and this alleged silversmith,” complained Henri, “we will have more than enough practice as artful dodgers.”

“Got us both going and coming,” gloomily added Billy, “and no show for argument.”

“We don’t have to respond to that message, anyhow.”

“I don’t know about that, Henri; we might be able to convince the crank at the shop that we haven’t any hold on underground wires, and so get rid of him.”

“And then prove an alibi when we meet that Cossack.”

Henri wore a grin as he put this extra spoke in the wheel of hope that his chum was turning.

Humor, however, was not catching to Billy this evening. The boys sat in silence at the mess table, and as silently stole away to bed.

The young aviators had no call for their services the next day, and Billy insisted that they play a quitting visit to the little shop in the square. Besides, he had urged, they were less likely to encounter the Cossack out in the big city than if they idled about headquarters. His motion prevailed, and shortly before the tower clocks sounded the twelve strokes, the chums were rounding the tall column and nearing the symbol of the silversmith.

Ricker had an assistant on duty in front this day, a wild-eyed individual literally overgrown with hair on head and face. When the boys entered the shop the queer-looking clerk spoke not a word, but simply pounded with his knuckles on the counter.

The proprietor of the place quickly appeared from a curtained recess at the rear of the shop, and crooked a finger in beckoning invitation to the visitors to come back and join him.

The hairy assistant went to the street door, and after peering up and down the avenue, nodded clearance to his chief.

The boys perched themselves on a couple of high stools in the work room, while Ricker leaned against a low and broad shelf covered with equipment of the clockmaker’s trade.

Billy was determined to settle matters there and then and get clear of an annoying and dangerous complication.

“This is the last time,” he bluntly stated, “that we will stand for a call here. Just as I told you before, there was a limit to our knowledge of Mr. Roque’s affairs, and as he did not choose to take us all the way, we have no desire to be dragged along by any stranger. Running aeroplanes is our business, and we are not seeking to acquire any other profession. So it’s farewell on the spot.”

Ricker showed a red flush of anger rising to his cheekbones, but he tempered his reply to the boy’s declaration. “Stick to your flying trade, young man, as you will, but on your service the Cause has a claim, and the penalty for ignoring that claim will be exacted to the last farthing, be it blood or bones.”

The implied threat put a tingle in Billy’s spirited makeup, and, jumping from the stool, he impetuously took up the challenge of the silversmith with wordy proclamation:

“When we leave this place, understand me, we don’t return, and, again, not the slightest bit of attention do we pay to any further communication from you. You get me?”