"This is all. I merely wished to advise you of what you will findwritten with invisible ink on the paper that will be placed in yourpossession when you set out on your return to America."

  The tapping ceased. Irving remained like a statue in his chair forseveral minutes. Then he arose, went to the window and pulled the shadeaside. The court was dark, save for a solitary dim light out at theentrance. He could just faintly discern the steel structure of the fireescape near the window.

  "That's the way he got up," he half muttered. "He stood there on thatlanding while he tapped his message. I wonder who he is and how hespotted me. He must be a very clever fellow. I really believe he'swhat he represented himself to be; and yet, it may possibly be a trap tocatch me. However, I don't see what I can do except awaitdevelopments."

  He went to bed and slept better than might have been expected under thecircumstances. But he had become so used to critical situations by thistime that he felt almost capable of sleeping peacefully on the "edge ofthe earth" with a torpedo for a pillow.

  Next day the mystery of the window-telegraph spy bothered him a gooddeal, even more than it did immediately after the fellow had "dotted anddashed" his message on the pane of glass.

  "I wonder who he was?" he repeated many times. "I wonder if he'ssomebody I'm in close touch with every day?"

  The suggestion caused him to watch narrowly every person in the officewith whom he did business for the German government. But the more hewatched, the more unsatisfactory the situation became. He continued hisfurtive outlook several days, but finally admitted to himself that theprospect of his efforts solving the mystery was anything but bright.

  Meanwhile the spy's preparations for a new excursion out into a broadfield of international espionage were rapidly drawing to a close. Thesurgeon at the hospital who had performed the skin-grafting operation onhis arm pronounced it sufficiently well healed, first, to warrant takingthe limb out of the sling, and then, a week later, for the removal ofthe bandage. There were a few slightly rough places here and there.around the edges of the patch, and one small scar at the lower end ofthe middle strip of skin where it had been twisted to cause it to lie"right side out" through the middle of the larger patch and make thelatter complete by meeting the outer edges that had been undercut anddrawn to it.

  All things considered, Irving was well pleased with the course of eventsduring his sojourn in the German capital. Although a number ofsituations had developed with rather dangerous aspect, he had pulledthrough all of them with apparent success. While he was still reportingdaily at the hospital for the dressing of his arm his lieutenancycommission was acted upon in the war office and was delivered to himthrough Mr. Herrmann.

  At last the day arrived for a windup of the young spy's affairs in theintelligence offices, and he was summoned into the presence of "thebaron" and Superintendent Herrmann. A third man also was present toreceive the young espionage student. He wore a navy uniform and wasintroduced as Capt. Bartholf of the submarine service.

  "You will go with Capt. Bartholf on board his boat," "the baron"announced, addressing "Lieut. Hessenburg." "He will land you on thecoast of Spain and from there you will go to a German consul and devisea method for getting you to Mexico and from there into the UnitedStates.

  "By the way," the high intelligence official remarked, suddenlyinterrupting himself and addressing Superintendent Herrmann; "how aboutthat letter that was being prepared for Lieut. Hessenburg to takealong?"

  "I'll see," replied Herrmann, as he started for the door.

  "Bring Strauss in with you," "the baron" called after him. "I may wantto ask him some questions."

  "Strauss!"

  The name echoed in Irving's brain with a succession of significantthrills. What did Strauss have to do with the preparation of the letterhe was to take with him? Was it possible--?

  He did not finish the sentence in words, but the idea was there andremained uppermost in his mind during the remainder of the session in"the baron's" office. Presently Herrmann returned, accompanied by thecard-catalog expert, who carried an envelope of ordinarybusiness-correspondence size in one hand. This envelope he laid on thedesk in front of the intelligence chief.

  The latter picked it up, looked keenly at Strauss and asked with likesharpness of voice:

  "This paper was prepared entirely by you, was it?"

  "Yes," the cataloger answered.

  "And it has been in no other person's hands at any time since you beganwork on it?"

  "No."

  "And you vouch for the accuracy and thoroughness of its preparation?"

  "Yes."

  "That's all. You may retire."

  Strauss left the room. "The baron" turned to Irving, handed him theletter, and said:

  "This innocent looking missive is of vast importance. It is addressedin cipher to a very important person in America who is high in theconfidence of the United States government. You have learned how to readthis cipher and will work it out for yourself. That is all. Good-by. Iwish you a continuation of the success that has been yours in aremarkable degree heretofore."

  Irving took "the baron's" offered hand and then left the officeaccompanied by Capt. Bartholf. As he went the name of Strauss continuedto ring in his head, together with this startling conviction:

  The catalog expert was the French spy who had tapped the "telegraphmessage" on his window at the rooming house!

  *CHAPTER XXXVII*

  *THE SUBMARINES*

  Lieut. Ellis of the Canadian army, alias Lieut. Hessenburg of the Germanarmy, had quite enough to think about as he left the office of "thebaron" in company with the submarine commander. Out in the receptionroom the latter took leave of him, saying, "Meet me at the Kaiserhof at9 o'clock tomorrow morning"; then the youthful spy, with acounter-spying commission from the enemy, went to his desk and began tomake arrangements for his departure.

  Mr. Herrmann selected from the office force a former soldier who hadlost one arm, and to him Irving made a brief statement of the work hehad been doing so that his successor might continue where he had leftoff. For a short time he debated in his mind whether to go to those ofhis fellow workmen with whom he had been more intimately associated andbid them farewell, but he decided that this would not be in harmony withthe "community conduct" of the officials and employes of the bureau. Infact, he had observed little in the association of the office that hadsuggested real community life. Everybody connected with theintelligence bureau seemed either to have been born with a coldfurtiveness of manner or to have developed an espionage attitude of thissort in the atmosphere of the greatest spy system the world had everknown.

  However, he disliked very much to leave the place for the last timewithout passing at least an "aufwiedersehen" to the one person there whohe felt certain was a friend of the great cause of human liberty forwhich the allied nations were fighting. But Strauss seemed disposed toignore him if possible. He passed several times near the expert's desk,but the latter pored more diligently than ever over his work. OnceIrving caught his eye and attempted to pass him a look of intelligentmeaning, but Strauss turned away quickly, and Irving left the buildingwithout saying good-by to one of the occupants.

  "A very cold-blooded business," he told himself. "My! I'm glad to beout of there. I'm afraid I'm not built along cold enough lines for aspy even in behalf of a great and meritorious cause. That fellowStrauss is an ideal spy. He must be the best any nation ever produced.He certainly has worked himself into a powerful position of confidencewith the enemy. But that was some chance he took when he tapped thatmessage on my window. I wonder if he expected me to discover who he wasafter he told me he was the fellow that prepared the letter that was tobe given to me. And when he assured the baron that nobody else had hadthe letter in his possession, nobody else remained for me to suspect.Well, he must know now that I spotted him; but he surely exhibitedextremely wise caution when he refused to recognize e
ven a significantlook from me. Good-by, Mr. Strauss, or whatever your name is. You weretoo shrewd to let me shake your hand, and cold judgment tells me youwere right. I hope after the war is over I may take a trip to Europeand look you up. But, judging from the way you looked at me, or avoidedlooking at me, I'm afraid you'd take advantage of the opportunity togive me a calling down such as few people have ever received. I'dprobably feel the knives of your sarcasm making ridiculous mince meatout of me."

  Next morning, promptly at the appointed hour, Irving was at theinformation desk of the Kaiserhof, asking for Capt. Bartholf. Thelatter was in his room waiting for the young intelligence officer. Twohours later, arrangements having been made for the transfer of baggage,the captain and the lieutenant were on board a train and headed for oneof the principal submarine ports of the German coast.

  The trip was uneventful, except that it afforded Irving an opportunityto make a study of the character of an official representative of thepolicy of ruthlessness of the military government of Germany. Capt.Bartholf was a fit exponent of this policy and exceedingly efficientbecause of the intelligence with which he could disguise the barbarousnature of his ideas. Hours before they reached the port of theirdestination, the spy was convinced that an enemy who fell into theclutches of this sub-sea commander might as well toss hope to thefishes.

  "I don't believe he'd take a prisoner if he could help it," Irving musedas a climax to his conclusions. "I'd never surrender to a man like himif I knew in advance what kind of fellow he was. It'd be a finish fighteven though there were no hope in it for me."

  They arrived at the seaport in the evening and took rooms at a hotel.Two days they remained in this city. The captain explained the delay bysaying that he was awaiting orders to start on a raiding cruise.Finally the orders arrived, and he announced that they would go on boardat once.

  Half an hour later they were at the docks, where a dozen U-boats werelined up, some of them taking in provisions and oil, or undergoinginspection and minor repairs. Irving's eyes were busy with new objectsof interest at this submarine harbor, for he had never before seen anundersea craft. Eagerly he took in the scene, regarding the variousobjects with more than the calculating interest of an international spy;and while in the act of boarding the vessel in which he was about totake his first submarine trip, he almost forgot, as the romantic thrillof the experience went through him, that he was surrounded by enemies inwhose hands his life would be worth only a volley of rifle balls if hisreal identity were revealed to them.

  *CHAPTER XXXVIII*

  *"KAMERAD!" AGAIN*

  "Shut off the power."

  Irving was in the conning tower with Capt. Bartholf and Lieut. Voltz ofU-31 when the latter, who was at the periscope, gave the foregoing orderthrough the speaking tube.

  They had been out all night and half the preceding day, running much ofthe time on the surface of the ocean in order to make the best possiblespeed. Irving had not a clear idea where they were, but presumed thatthey must have passed a considerable distance beyond the western end ofthe English channel.

  Lieut. Voltz gazed again into the glass of the periscope after givinghis order to the engineer. He had had his hand on the lever at hisright and with this had turned the periscope tube so that his eye couldsweep the horizon. Now, however, he had discovered something, and he nolonger moved the lever except occasionally little more than a hair'sbreadth in order to keep the object of interest in view. After a fewmoments of further careful examination and reference to the telemeterattachment to determine the distance away of the discovered object, hecalled again into the speaking tube.

  "Go down four fathoms."

  Then turning to Capt. Bartholf, he said:

  "There are two vessels about five knots a little south of west fromhere. One is probably a convoy."

  "Run about three knots closer and take another peep," the captainordered. "Did 17 and the 23 sight them also?"

  "I think so. Seventeen just went under."

  Irving understood this question and answer to refer to two other U-boatsthat accompanied No. 31 on this trip. Meanwhile the latter submerged tothe depth ordered by Lieut. Voltz.

  Twenty minutes later the periscope was again a few feet out of the waterwith the lieutenant's eye glued to the glass and his right hand workingthe lever.

  "Let me have a look," said the commander.

  He gazed a minute into the glass and then said:

  "I'm going to try to get that convoy first and then the other, whichappears to be a hospital ship."

  Irving shuddered.

  The order was again given to submerge. The lieutenant seemed to bedoing all the work of lookout, pilot and operating master, for he wasbusy at the steering wheel, periscope, and speaking tube almostsimultaneously much of the time. All these were within easy reach fromone position. The "sub" arose several times near enough to the surfaceto enable the lieutenant or the captain to take a peep at theprospective prey, and then down again it would go. At last, underdirection from the captain, the lieutenant gave this order through thespeaking tube:

  "Have the men slide a torpedo into one of the forward tubes."

  Eager to witness this operation, Irving sprang to the stairway and wassoon down on the lower deck. There he saw several members of the crewremove the safety attachment from the nose of a sixteen-footphosphor-bronze torpedo, which was seventeen or eighteen inches indiameter, and slide it into a tunnel-like hole in the midst of a maze ofoperating machinery. A minute or two later the order was given to"shoot," and out it went, under initial propulsion from a compressed airengine.

  Then the order to submerge was given again, and away they went southwardat full speed under three fathoms of water. Ten minutes afterward theperiscope peeped up over the surface of the sea once more, and Capt.Bartholf had his eye glued eagerly to the glass.

  A moment later he gave a yelp of delight, and Irving knew that a hit hadbeen scored.

  "We've hit 'em both fine!" the commanding officer exclaimed. "One ofthe other boats must have fired a torpedo about the same time we did.Both of those ships are going down."

  It was not regarded safe to show the hulks of the submarines above thewater yet, however, for fear lest the convoy hit one or more of themwith a shell as a last living act of revenge. But they did not have towait long, however, for the doomed vessels sank rapidly.

  Then all three submarines showed themselves on the surface and Irvingwas delighted to observe that apparently all of the sailors, soldiersand nurses that had been on the hospital ship and the convoy were now inlifeboats, which were being rowed with frantic desperation away from theU-boat-infested spot.

  "Follow them up and let's see what they look like," Capt. Bartholfordered, with a kind of gloating glee.

  All three captains seemed to be of like mind, for all three U-boats tookthe same course and ran up close to the crowded lifeboats. Severalofficers and members of the crew of each of the submarines appeared onthe outer deck to view the results of their uncontested victory.

  Suddenly there came from one of the boats a call that thrilled andchilled Irving with a sense of awed familiarity.

  "Kamerad!"

  Where had he heard that cry in that tone of voice before? He could notdecide on the moment, and yet he was apprehensive of an unpleasantdiscovery.

  The captain of U-31 determined to investigate and ordered the lifeboatfrom which the hail proceeded to come alongside. The occupants could donothing more sensible than obey. As it approached a young man with anempty left sleeve arose and repeated his appealing cry, and Irvingalmost dropped in his tracks.

  The one-armed fellow was Adolph Hessenburg, alias Tourtelle, the formerCanadian lieutenant of the tattooed cubist art cryptogram. Undoubtedlyhe was being sent to England to be held there for a determination of hisfate after information had been received regarding the success orfailure of his substitute spy's mission within the German lines.

 
*CHAPTER XXXIX*

  *"ACCIDENTS WILL HAPPEN"*

  If anybody had observed the precipitation with which Irving dived downthe hatchway of U-31 a moment or two after he recognized the "cubist artspy," there is no doubt that the observer would have been impressed withthe mystery of the proceeding. As it was, all of his boche companionson the outer deck were too much interested in seeking an explanation ofthe "kamerad" cry from the midst of a boatload of enemy soldiers andsailors to give attention to anything less than the explosion of a bombon their own vessel.

  Irving meanwhile picked up a sou'wester that he found on the lower deck,put it over his head so that it partly covered, shaded, and henceconsiderably disguised his face, and then returned to the outer deck.True, the weather was not stormy, but the air was chilly and the"cloudburst hood" added considerably to his comfort.

  The real Hessenburg had been assisted on board and was being questionedby Captain Bartholf. Irving heard the latter ask him his name, and thensuddenly something happened which the trembling spy has ever sincedeclared undoubtedly saved his life and some very important informationfor the Allies.

  What caused the sudden lurch of the submarine was not subsequentlydisclosed. Possibly one of the men below, accidentally or thoughtlesslymoved a lever or wheel that resulted in a momentary spasm of mechanicalaction. At any rate, all on the outer deck were dancing around forseveral seconds to preserve their balance, and one of them was not assuccessful as the others. That was Hessenburg, who was thrown violentlyagainst the low railing so that he struck his head on one of the ironstandards or posts.