Chapter XV: Another Mystery Unraveled

A piece of transparent celluloid, furnished by their host from a broken side curtain of his automobile, supplied Captain Hardy with the material needed for making the disc that was to be the key to future communications of the enemy. Carefully he cut the celluloid the size of a dollar, then marked the exact centre of it. Next he clamped the disc on the captured coin. Between the rows of letters he scratched in the straight radius lines--the spokes of a wheel. Then Captain Hardy put the end of one arm of his dividers in the dot at the centre of his disc, and swept the other arm around, scratching a circle just outside the first letter in the message--the innermost T. Examination showed that this circle fell just inside of the second letter in the message--the W. Adjusting his calipers, the draughtsman made a second circle, just outside of this second letter. A third circle fell between the first O and the second T of the message. So Captain Hardy continued, each succeeding circle falling just outside of the succeeding letter in the message. When he had finished, his disc contained twenty-three concentric circles, between which could plainly be seen the bright dots or scratches in the dingy dollar.

"Whew!" said Captain Hardy, as he laid down his dividers. "That's pretty fine work--twenty-three circles within a space of an inch and a half. I'll wager a watchmaker made their pattern for them. The solid parts of their metal discs can't be much larger than these lines I have scratched on the celluloid. You were right when you named it, Willie. The parts of it must be just about as thick as a spider-web."

The boys passed the dollar and its superimposed disc from hand to hand, examining them with eager interest.

"Suppose they wanted to send a message with more than twenty-four letters in it," said Roy. "How could they do it? I'm sure some of the messages we intercepted had more than twenty-four letters in them."

Captain Hardy picked up the disc-covered dollar and studied it intently. "I suppose," he said after a time, "that they would put more than one dot in the same circle, and the dots would be read in the same way they are now. The one to be read first would be nearest the centre of the coin, and so on. Or they could write on several coins, each coin being numbered in some way, and corresponding to a paragraph in a composition."

Again he studied the dollar closely. "Clever!" he said admiringly. "Mighty clever! Who would ever dream that those tiny scratches meant anything? Many a time I've seen a dollar scratched and nicked a deal worse than this one is, though they've evidently chosen a battered one so that their own marks will be less noticeable. Why, that coin might have passed through our hands a hundred times, and if we had not actually seen it marked we should never dream it said anything other than 'In God We Trust.' We've had a great stroke of luck, boys."

He paused and meditated. "I wonder if it is luck," he went on. "May not the motto on that dollar explain our good fortune? Perhaps it is Providence rather than blind luck that has guided us. At any rate let us hope so. Now I'm going to report to the Chief. Won't he get a surprise?"

And Captain Hardy left his subordinates, chuckling at the prospect of the Chief's astonishment.

But it was Captain Hardy who had the surprise. Instead of the stern, silent, brusque man he had become accustomed to, Captain Hardy found the Chief smiling and talkative. As his eye fell on Captain Hardy, the Chief rubbed his hands with apparent satisfaction. Evidently something had happened that had put him in an extremely good humor.

"Ah! Captain Hardy," he said, "we beat you to it this time. I already know what you have come to tell me. But I am glad to see you just the same. One of our operators," continued the Chief, "happened to be shifting his tuning-coil when our friends, the enemy, were sending their message yesterday afternoon, so that I have all the latest spy news."

He paused and smiled at his astonished visitor. "You see," he added, a real Irish twinkle coming into his eyes, "the secret service is not so slow after all."

"Congratulations!" cried Captain Hardy, in the same spirit of fun. "The secret service is improving. But I have some news that may make my trip not altogether without interest to you."

The Chief interrupted him. "We know who the man is that has been telephoning to your Staten Island grocer about sugar," he said. "When he called up yesterday afternoon, the telegraph operator flashed the tip to my man, who happened to be on duty within a few doors of the place the man was talking from. Of course my man spotted him and trailed him. The fellow proves to be a clerk on one of the piers where transports are loading. His position gives him no opportunity to get aboard the ships, so he does not know what goes into the transports. But he does know how many boats are loading and about when they will sail. Evidently he is afraid to telephone directly to any of the better known German agents we are watching, and as far as that goes he may not even know who they are. I suppose this plan of communicating with Staten Island is to give the spy there a chance to observe the transports as they sail from the harbor, and see if he can learn anything about their cargoes. We have put this steamship clerk under observation and from now on he will be watched night and day. We're closing in on them fast."

"Congratulations!" cried Captain Hardy again, this time in sober earnest. "You are doing excellent work. Now when you hear what we----"

Again the Chief interrupted him. "Oh! I haven't told you all _my_ news yet, not by a long shot," he said. And again the head of the secret service rubbed his hands together. "We know who the driver of the wireless motor-car is. I don't mean we know the name he's using. Anybody could get that out of a directory. It's Sanders. But we know who he really is. And that's why we feel so good to-day. He's a man we've been looking for for months. He is one of the German agents implicated in the papers we seized in Wolf von Igel's office. The secret service has been more than anxious to discover his whereabouts. Now we have him, for he's under observation and cannot escape us.

"He came to this country about a year before the war started," continued the Chief, a gleam of satisfaction shining in his eyes, "and bought out an insurance agent who made a specialty of insuring suburban properties. From the beginning, he made a practice of visiting the properties that he insured. This took him about a good deal and gave him an excuse for being so much in a motor-car. Ah! What an ideal situation for a spy! Clever, aren't they?"

But the Chief gave his visitor no chance to reply to his query. Smiling again, he went on, "But even this is not all. Of course you understand, Captain, that your boys are not the only amateurs helping us out in this pinch. Ever since we became convinced that the Germans have a line of secret wireless stations by which they are relaying news to their agents in Mexico--for we're morally certain that is where these messages go--we've had trusted amateurs helping us just as you have helped us--by listening in. Some of them have been at it for weeks. When we could get no trace of secret messages along the direct route to Mexico, where they would naturally have their stations, we began to suspect that the Germans were using a round-about route in the hope of deceiving us completely."

"And you've located some of them?"

"Exactly. Your boys will tell you that yesterday was one of those days when radio communication is at its best--when an operator picks up sounds that at other times he could not possibly hear. The result was that we picked up yesterday's secret message at half a dozen different points. Where do you think the first one was?"

"Give it up."

"Buffalo--north instead of south. Clever, eh? Then we got it near Detroit, and Milwaukee, and Omaha, and Santa Fé. Finally one of our listeners picked it up at Socorro, a place about one hundred and seventy miles north of El Paso. Now we know the line of their stations. We'll set a regiment of amateurs to listening in along that line and we'll locate every station in it in no time. Then we'll grab all their agents at the same time in one big raid and wipe out this spy system for good."

"That is great news," said Captain Hardy, his eyes sparkling with interest. "Great! You certainly have cause to feel good."

"For a little while," replied the Chief, "I thought I had even more good news. But it proved to be a false alarm."

"What was it?" inquired Captain Hardy as the Chief stopped speaking.

"Oh! Simply this. Some time ago one of our listeners caught an earlier message near Socorro, which gave us a hint as to where the messages were crossing the border. We at once sent a number of expert army wireless men into that part of the border region to listen in. One message was picked up at a point fifty miles north of the boundary, but it was very faint. Along the line itself the radio men have never detected a sound. Yet your boys are intercepting the messages here, so we know that they are being sent regularly. That made us think that perhaps the messages were being telephoned the last lap of the journey and carried over the line by a person."

"I have no doubt that your theory is correct," said Captain Hardy.

"Well, last night we thought for a time that we had the man who was carrying the messages. When my operator here picked up the message yesterday afternoon, I instantly sent a message to my subordinate in charge of the work in the El Paso district, telling him of the sending of the message and urging extra vigilance. Yet not one of the radio men heard a sound. But in the middle of the night my men grabbed a Mexican who had slipped past the armed guards and was starting to wade across the Rio Grande to Mexico."

"Excellent!" cried Captain Hardy.

"Good enough as far as it went," said the Chief, with a wry face, "but it didn't go far enough. The fellow was only a smuggler."

"Are you certain, Chief?"

"Sure as preaching, worse luck."

"Was the man searched thoroughly?"

"Now, Captain, what do you think the secret service is, anyway? Was he searched! It would make your eyes pop out if you'd see the way we go through a man. We strip him and give him a lemon bath to bring out any secret message that might be written on his skin, and we take his clothes apart scientifically, I tell you. No, this fellow had nothing incriminating on him. After a grueling examination, he admitted that he had crossed the line to smuggle in some tobacco. However, it's only a question of time until we _do_ put our finger on the missing link. Then for a great raid!"

"How I shall welcome that day," said Captain Hardy. "This spy business is never absent from my thoughts, with its menace to our boys on the ocean."

"I think that you will soon be free to go back to the army," said the Chief. "Your work is about done. This thing is coming to a head fast now. But of course I shall need your boys to listen in for a time, so that we can know what the Germans are sending. But there will probably be no more real work for you. We certainly are grateful for the help you gave us, though. We have been terribly crowded these last few weeks."

In his pride at the work his boys had done, Captain Hardy momentarily forgot the errand that had brought him to the Chief's office. He stood before the head of the secret service, smiling happily. Again he began to think of that long chain of secret wireless stations, so sinister and so menacing, with voice crying treachery to voice through the air, carrying word that at any time might cause the murder of thousands of our brave soldiers. Mentally he journeyed along the line of those stations--from New York to Buffalo, to Detroit, to Milwaukee, to Omaha, to Santa Fé, to Socorro, to Mexico. With quick imagination he pictured the scores of little secret stations needed to carry those treacherous messages across so vast a span of earth. Some he saw skilfully hidden in forests, as the wireless had been concealed at the Elk City reservoir. Some he pictured in abandoned farmhouses. Others he saw in barns, in the stacks of ruined factories. And some he imagined as flinging their voices abroad amid the burning plains of the arid border-lands. But he could not picture to himself the invisible messenger that took the word across the boundary. He could not fathom the mystery, he could not picture to himself the missing link in the chain. As was always the case with him, his mind began at once to grapple with its problem--in this instance the riddle of the missing link. He actually forgot where he was.

"I wonder," he said, though he was really talking to himself, "what was done with that smuggler."

"We clapped him into jail to await trial for smuggling," said the Chief.

Captain Hardy came to himself with a start, and smiled. "You say they got nothing incriminating on him," he remarked. "Did your men find anything at all?"

"Only the money he had gotten for his tobacco."

Mechanically Captain Hardy had thrust his hand into his pocket. As the Chief answered the question, Captain Hardy's fingers came in contact with a silver dollar and a disc of celluloid. Of a sudden an eager light flashed into his eyes. "What kind of money did that Mexican have?" he demanded.

"Some silver," said the Chief indifferently.

"Of what denominations?"

"Dollars. He had three of them."

"What was done with that money?" asked the captain with an earnestness that was almost tragic.

"Oh! The greaser made such a disturbance that the jailer let him keep it. He's got it with him in the jail."

A great sigh burst from Captain Hardy's lips. "Telegraph your men instantly," he cried, "to get those dollars. That Mexican is no smuggler. He's a spy. He's the man who carries the messages across the border. The messages are on the dollars. And here's the key to the cipher!"

And he drew from his pocket and laid before the Chief a battered silver dollar and a curiously marked celluloid disc.