"We will go direct to Col. Evans' headquarters," Lieut. Osborne announced shortly after the return trip had been begun. "He asked me to report back to him as soon as possible."

The trip was soon made. The colonel's headquarters were less than a mile behind the rear line trenches, and the road to this point was in fairly good condition.

Irving felt a deep interest in this visit aside from the bearing it had on the matter under investigation. He had never seen a colonel's headquarters and was curious to know what appearance such a place might present.

He was not greatly surprised to find it a dugout, although he had not pictured it such in his mind. The first suggestion that had offered itself to him was that the head of the regiment probably had stationed himself in the palatial residence or chateau of some wealthy fugitive civilian. However, when the truth appeared to him with the most commonplace simplicity, he decided that it was the very thing that he ought to have expected.

The dugout was a two-room affair in the side of a hill on the outskirts of a small village. The hill was covered with fruit trees and berry vines, affording an excellent camouflage. One of the rooms was occupied by the colonel and the other by his orderlies. The walls and roof were of concrete, thick enough to resist heavy bombing from the air. Other attaches of this headquarters were housed in several homes of the otherwise deserted village.

The commander of the regiment received the visitors in his elaborately furnished living room, bedroom and dining room. Lieut. Osborne began at once a rapid account of the interview he had had with Second Lieut. Tourtelle, or Hessenburg. The colonel listened attentively, every now and then casting a sharp and sometimes lingering glance at Private Ellis, who had all he could do to suppress the anxious eagerness he felt relative to impending developments. Naturally, as he had rather dubiously offered the original information that led up to the partial disclosure of extensive spy activities, he felt as if his whole future depended upon the full success of the investigation.

Lieut. Osborne opened the box containing the tattooed message and took it out of its salt packing. Col. Evans examined it curiously while the reporting officer explained all he knew about it, calling attention to the telegraphic dots and dashes running around the numerous "cubes."

"We ought to get somebody who is skilled in cryptographic work busy on this at once," said the colonel. "I've been in communication with the brigadier general's headquarters and suggested that to them, and now that I have this in my possession, I'm going to urge it stronger. I'll get them on the wire again."

They were seated at a table at one side of the room, and as he spoke, the regiment commander cranked the telephone box at his right and lifted the receiver to his ear. The conversation was short, for the intelligence department at the brigade headquarters had been busy on the colonel's suggestion and already had found an expert qualified to probe the mystery of the cubist cryptogram. He would start at once for the regimental headquarters.

"Just wait here till our cryptologist arrives," said the colonel, after reporting the result of his conversation over the telephone; "and maybe he'll be able to clear up matters so that we may begin to see bottom."

The expert, Lieut. Gibbons, attached to the divisional commander's intelligence staff, arrived half an hour later, and the spy story had to be told all over again for his benefit, while he examined curiously the "freak-art camouflaged message."

"I may be able to work this out in a few hours, and then again, it may take several days," he said. "I'd better take it with me back to headquarters and work on it there and report back results as soon as I get them."

The colonel assented to this and the expert prepared to depart with the cubist cryptogram in his possession. Then the regimental commander turned to the officer and the private and said:

"Lieutenant, you will return to your company. I will call on you when I wish to communicate with you again on this matter. Private Ellis, you will remain here. I can use another orderly, and, besides, I'd like to have you close at hand in case of further developments in this spy investigation. By the way, can you operate a motorcycle?"

"Yes, sir," Irving replied.

"Good. You can be useful at once. I have some papers that I want delivered to the brigadier general. You may follow Lieut. Gibbons' automobile and learn the way. He goes past the brigadier general's headquarters."

A motorcycle was soon produced and Irving, after a hurried examination of it, announced that he understood it thoroughly. A minute later he was in the saddle and "lickety-chugging" along after the intelligence official's automobile.

And meanwhile there was buzzing in his brain this new wonder with eager expectation:

"What was the real purpose of Col. Evans in keeping him at headquarters"? Was that officer likely to have further army detective work for him to do?

Already he was beginning to feel like a government secret service man, and he longed to be of further service to his country and the cause of world freedom in this romantic line.

He little dreamed how far beyond the scope of his saner imagination his patriotic longing was to be realized.

CHAPTER XVI

A STARTLING ANNOUNCEMENT

Three days later Col. Evans summoned Irving into his dugout office and said to him: "Well, the cubist cryptogram has been read."

The officer smiled with a kind of grim exultation as he spoke. Then he added:

"And it contained very important information."

"I'm glad of it," the boy answered simply, although he felt almost as if he would burst with a "hurrah!" that threatened to explode within him.

"Of course you are," the commander concurred. "And I suppose you'd like to know what's in it."

"Naturally," Irving replied; "but I doubt very much if you are going to tell me."

"Why?"

"Because, in the first place, it's none of my business as a private; and, secondly, I presume it is information of a character that the war department wishes to keep secret."

"Right you are, Ellis. That's the main reason I put the matter up to you. I wanted to find out what you thought of it. But there's another reason why you shouldn't know the contents of that message, and I'll tell you that later. Meanwhile, I have another important matter that I want to quiz you on. Do you want to go back to the trenches?"

"I'm perfectly willing to go back if that is the best thing I can do," Irving answered readily. "But I'll say this, that if there's any other place where I can be of greater service, I prefer to be sent there. It's a question of service pure and simple with me. Naturally, I have my selfish preferences, but I manage to suppress them."

"Have you any idea where you could be of greater service than in the trenches?" asked the colonel.

"I'll answer your question in this way: I'm sure that the time I spent helping to run down a dangerous spy was put to much better purpose than it would have been if spent in the trenches, although I think I did some good work out in No Man's Land in front of the trenches. But, of course, there's no more of that kind of work left for me to do."

"Are you sure about that?"

Irving looked curiously at the putter of this question, considered a moment or two, and then replied:

"No, I'm not; but I don't know of anything more."

"Suppose some more of that kind of work should be found, would you like to do it?"

"Surely."

"Irrespective of the size of the task or the danger?"

"I don't know how I could find anything much more dangerous than that skirmish in No Man's Land," Irving replied slowly. "The other part of your question I don't wish to answer rashly. Tell me the task, and I'll tell you if it's too big for me."

"That's the very answer I wanted you to make," said the colonel, almost eagerly. "Now, suppose we should ask you to go over into Germany on an important spy mission, how would that strike you?"

This was something Irving was not looking for, and he was so astonished that he did not answer for several moments. Then he said:

"It would strike me all right."

"Suppose you were given a credential that would effect admittance for you into high official circles-would you go there and attempt to obtain information that might be available, because of your credential?"

"Yes, sir," Irving replied firmly.

"What do you think of that stunt of tattooing a message in the form of a freak art production on the arm of Lieut. Tourtelle?"

Irving smiled.

"Of course," he said, "it was clever and under ordinary circumstances ought to have been successful; but I'd rather not go through life with a thing like that on my arm. It might brand me as a freak, if not something worse."

"I don't blame you," returned the colonel, but as he spoke a peculiar shrewdness lighted his eyes, causing the boy to wonder a little. Then he added: "Still, it might be possible for one to submit to such nonsense if thereby he might advance a great and worthy cause."

"Sure, that's quite possible," Irving agreed; "but I don't see how Tourtelle, or Hessenburg, can claim any such motive."

"No, but if he had done it for his own country, the British empire, to advance the cause of human freedom, what then?"

"Well, in spite of the ridiculous appearance of the picture on his arm, I'd say he ought to be proud to keep it there. I would. I think I'd be proud to show it. It would be something to show and tell about to-to-my great-great-grandchildren when I got old, you see," Irving finished with a really illuminating smile.

"I think I've quizzed you far enough on this subject," Col. Evans announced at this point, throwing off the manner of vagueness that had hitherto characterized a good deal of his conversation, and speaking with unmistakable directness. "I'm now going to ask you to consent to have that cubist picture tattooed on your arm."

Irving looked in astonishment at the commanding officer of the regiment, being scarcely able to believe his ears. Surely the proposition was nonsensical. And, yet, this was no occasion for nonsense. But the boy's wondering conjectures were interrupted by the officer, who was adding to his last announcement.

"After the art work on your arm is finished," he said, "I'm going to send you into Germany to find out some things we want to know."

"Yes?" Irving responded, with a rising inflection that carried with it a suggestion of an interrogation.

"Yes," the officer continued; "I want you to take the place of the spy whose tattooed arm had to be amputated."

CHAPTER XVII

PARACHUTE PRACTICE

Private Ellis looked hard into vacancy and thought just as hard for half a minute; then he said:

"I get you, I think, Col. Evans, all except one point; and that, I suppose, would come to me all right if I knew the contents of that tattooed message."

"No, you wouldn't," the colonel returned quickly. "It wouldn't do you a bit of good."

"I'd know whether it's important," Irving insisted.

"I can tell you that much," was the officer's reassurance; "and then you're no better off. It's of vast importance and would be of incalculable value to our enemies if it fell into their hands."

"Then there's only one explanation of your proposition," Irving concluded. "You will change the dots and dashes so that they will convey information different from that originally intended."

"Good!" exclaimed the colonel. "You'll do all right. Are you willing to undertake it?"

"I am," said Irving.

"Very well. So far so good. Now I'm going to test your nerve some more. Look out, for this is going to be a corker. If you drop, you'll drop hard."

"I'm waiting," said the boy, with a kind of gritty grin.

"All right. Would you dare make a descent with a parachute from an altitude of several thousand feet?"

This was a tester, indeed. Irving knew it the instant the last word of the question left the colonel's lips, but he did not flinch.

"Of course, I ought to have some preparation for such a feat," he replied. "I've never been up in an aeroplane."

"To be sure," Col. Evans agreed, with a vigorous nod. "You'll get all the schooling necessary. You'll start out on the venture well equipped. I'm going to send you to the aviation field near brigade headquarters, and there you'll learn to do your umbrella stunt. Then you'll come back here and go through some more preliminaries. The work of a spy, you see, is just as much of a science as the handling of an army."

That ended the interview, and an hour or two later Irving started in an automobile for the aviation field with a note from the colonel to the flying commander. There he was placed under an expert, and his schooling in the art of dropping from lofty heights began.

Private Ellis did not clearly understand just how all this program was to be carried out, but he had no doubt that Col. Evans had a complete plan in mind and that the missing details would fit in well with what had already been revealed to him. So he went about his new work confident that the outlook for success was good.

His training at the aviation field lasted a week. During that time he made half a dozen descents by parachute from various altitudes. The last descent was from a height of 3,000 feet. By this time the experience had become almost as commonplace a thriller as coasting on a long toboggan slide or "dipping the dips" at an up-to-date amusement park. He had never dreamed that descending with a parachute could become so matter-of-course a performance.

"I understand now how circus people can look on their death-defying stunts without being awe-struck with their own daring," he mused after he had floated down the fourth time at the rate of three-and-a-half feet a second. "Just think of it: a good swift sprinter would run a hundred yards in about one-third the time that I take to fall thirty-five feet. This is quite a revelation of physical science to me."

Irving was by nature a very observing youth. His instructor was something more than a mere bird-man, for he had studied aviation as a mathematical, as well as a physical, science. He showed the boy how to figure out the rate of falling after being given the diameter of a standard-made parachute and the weight of the aeronaut.

The parachute with which the young spy-student got his experience as a diver from the sky was one of several supplied for experimental work following reports that the enemy had perfected a similar device which had proved successful as a life saver in air battles. But the experiments of Allied aviators had not proved sufficiently successful to warrant providing all air fighters with "high-dive umbrellas." Descents could be made with reasonable assurance of safety from aeroplanes flying in good order, but if a pilot lost control of his machine the chances were small that he or his companion gunner or bomb dropper would be able to leap free from the struts and other framework with a parachute.

Irving would have liked to learn to pilot an aeroplane, but there was not time enough for him to take up that study. Indeed, before half the week had elapsed he decided he could like no occupation better than that of an aviator. He saw several expeditions start out to meet the enemy at the front, and also saw them return, followed by the announcement on two occasions that several of the British and Canadian flyers who had gone out to meet the foe, full of confidence in their own prowess, would return no more. They had been either shot down or forced to descend within the enemy's lines.

Nothing was said at the aviation field regarding the reason for the training that was being given to Private Ellis. No questions were asked and Irving did not volunteer any information. At last the instructor stated to the boy that he had completed his course and had learned his lessons well, and that he was now at liberty to seek further directions from the colonel. He accordingly returned to the latter's dugout.

Col. Evans asked him a number of questions, and then said:

"I want you to return to the field hospital and get some more information from that spy, Tourtelle, or Hessenburg. And in getting your information, remember that you are to impersonate him on the other side of the Rhine. Now, this is going to be a test of your spy-intelligence. Let's see how well equipped you can return here after your next interview with him. Do you get me, or must I give you some tips?"

"Don't give me any tips, but let me show you what I can do," Irving replied. "If I fall down on this mission, you'll know I'm not the fellow for the job."

"All right," said the colonel. "I've telephoned for Lieut. Osborne to come here and accompany you again. But this time, remember, you are to do the quizzing, and the lieutenant is to report to me how efficiently you went at it."

"I'm glad to be put on my own responsibility, sir, before I drop down from the clouds into the midst of the enemy," the boy said grimly.

CHAPTER XVIII

STUDYING TO BE A SPY

An hour later Lieut. Osborne arrived at the colonel's headquarters, and he and Private Ellis started at once for the field hospital. There they found Hessenburg, alias Tourtelle, much improved physically, but not a little nervous regarding his own rather precarious prospects. Instead of being an officer helping to direct, in his small way, the battle against the autocratic presumption of a great military power, he was something more than an ordinary prisoner of war-a trapped spy, who had conspired with others for the downfall of his own country. With seemingly genuine repentance, he exhibited much eagerness to give all the information possible in order to induce leniency for himself from a court-martial.

"I am instructed by Col. Evans to make this statement to you as coming from him," Irving announced early in the interview: "He desires all the information you can give him regarding your program that was to have been followed if you had succeeded in making your way beyond the enemy lines. He has certain plans in view, the success of which will depend largely on the correctness of your information. If you should misinform him, through us, those plans undoubtedly would fail. Moreover, if any enemy spy should get a tip through you or anybody else, that the information supplied by you was being used to attain important ends, those ends probably would never be reached.

"What we must have from you, therefore, is the truth, and the whole truth. To insure his receiving this, Col. Evans has asked me to inform you that the only thing that can save you is the success of his plan. If the plan fails, he will assume that the blame is yours and you will be shot."

Irving paused a moment, and Hessenburg seized the opportunity offered to interpose thus:

"You mean to say that he will have me shot for something for which I'm not the least responsible?"

"Not at all," Irving replied. "You will be shot for being a spy, which has already been proved against you. But if you're careful to tell us the truth, even though I don't cover some of it with my questions, your chances to escape that penalty are good."

"I understand," said the spy. "Fire away. I'll do the best I can."

The three were seated about a small table in a small room selected for the purpose. The door was closed. Irving drew a note-book and pencil from his pockets and prepared to jot down reminders of the information received by him.

"First," he said, "we'll all talk in low tones to prevent, if possible, anybody's overhearing us. Now, begin by telling me what was the extent of your acquaintance with spies in Canada and their system of operations."

"My acquaintance with those people and their affairs was very limited," Hessenburg replied. "I can't even say that my uncle was, or is, a spy, although it would be natural to suspect him. Government agents watched him pretty closely, and it's possible that he didn't actually do anything that would call for his arrest. But I'm pretty certain he knew a good deal more than I did. I think he knew all about my affair and approved of it. To tell the truth, I believe that it was through him that the spy organization learned that my sympathies were treasonable and decided to approach me on the subject of making a spy agent out of me.

"It was the man with whiskers at the hospital who first broached the subject to me: You seem to have a pretty complete report of that affair. That man was a physician, and I got acquainted with him while making business trips to the hospital for my uncle. He learned that I was an art student, and one thing led to another, until he knew I wanted England and France to be defeated and was willing to do anything I could secretly to bring that about. After that it didn't take him long to persuade me to be the bearer of a tattooed message on my arm into Germany. The other fellow who helped tattoo the message was the artist, an architectural draftsman with considerable skill at free-hand drawing."

"What are their names?" asked Irving.

"Dr. Adolph Marks and Jacob L. Voltz."

"What is your uncle's name?"

"Ferdinand J. Hessenburg."

"What does the 'J' stand for?"

"Johan."

Irving put a long string of questions of this kind, and thus obtained much detailed information regarding the spy and his family connections and home surroundings, also concerning the art school he attended in Toronto. He made copious notes of the answers, so that the process of questioning the confessed enemy agent was necessarily much slower than it otherwise would have been.

"I'm up against one difficulty that I'd like to clear away," the inquisitor mused in the course of his examination of the wounded "second looie"; "and that is the fact that this fellow is an artist and I am not. Suppose when I get over in Berlin, some wise fellow, full of information from Canada, should ask me to paint a cubist picture. What would I do? I must find out if there's any danger of my being asked to do anything of that sort to test my identity."

He continued his questioning thus:

"Did those two men who tattooed that picture on your arm know that you were an art student?"

"Oh, sure," Hessenburg replied. "That's how they happened to suggest the art method of conveying the message."

"And how about your credentials, your identification when you got into Germany? How were the German officials to know who you were, that you weren't a fake?"

"By the message itself."

"You think your instructors believed that was enough?"

"Yes, they said so. We had that question up for discussion. I raised it myself."

"How did you raise it?"

"I wanted them to get word to Berlin by another route to look out for me, but they said that would involve a danger that they were trying to avoid by the tattoo method. If they tried to get a wireless code message to Berlin, it might be intercepted and deciphered, and then a thorough search would be made for me."

Irving was much relieved by this statement. There was no reason to suspect Hessenburg of trying to deceive him in this regard. The spy could have no grounds to suspect that his inquisitor was planning to take his place and carry an altered copy of the cubist me