“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!