As the drone of the motor died away in the distance, Johnny became conscious once more of the sentry-like tread from without.  
“Who can that be?” His heart went into a tailspin. He was alone, unarmed. He thought of the gamblers, of Greasy Thumb and his gang, and of the money in his pocket, that roll of bills which belonged—well, to whom did it belong?
 
Regaining control of his nerves, he crept noiselessly to the front of the tent, then cautiously opened the flap a narrow crack.
 
22
The sight that met his eye caused him to start back. Barely did he escape making an audible exclamation of surprise and alarm. There, walking slowly back and forth before the tent, now in the shadows, now in a narrow spot of light, was as strange a figure as one might hope to see. Wrapped from head to ankle in a long gray coat—or was it a robe?—wearing gray shoes, gray gloves and with a gray slouch hat pulled down over his eyes, and with something that at least resembled a gray beard hiding the lower part of his face, this tall, slim man, if man it were, presented an awe-inspiring spectacle.
 
“The Gray Shadow!” Johnny whispered with a shudder. Twice before, each time in the heart of the city, he had caught a fleeting glimpse of this curious figure. Each time he had been in grave danger. With the passing of the Gray Shadow the danger, too, had passed.
 
“And now it is here,” he thought to himself. As he stared, the Gray Shadow disappeared into the depths of deeper, darker shadows and did not return. At the same moment Johnny thought he discerned figures retreating in the opposite direction.
 
“Queer doings!” he muttered to himself.
 
23
A moment later a low whistle sounded at the back of the tent. It was followed almost at once by sounds of stealthy movements. This time Johnny did not quail. He knew that whistle. Two minutes had not passed when two old friends, Drew Lane and Tom Howe, came creeping in on hands and knees. They had lifted the canvas at the back and entered unannounced.
 
“Did you see it?” Johnny whispered.
 
“See what?” Drew Lane demanded.
 
“See him?”
 
“Him or it? What are you talking about?”
 
“The Gray Shadow.”
 
“Again?” Drew Lane’s tone was filled with doubt. He had never seen the Gray Shadow. Being a detective, and a good one, he believed only in that which he had seen with his own eyes.
 
“Oh, I saw him right enough this time!” Johnny declared. “Walked across in front of my tent twice before he disappeared; exactly as if that were his business. Queerest sight you ever could look at. Didn’t seem human.”
 
24
“All right,” Drew Lane agreed, rather sharply. “You may have your shadows. We’ll deal with real crooks. That’s a detective’s business. Greasy Thumb and his gang are gone.”
 
“Gone!”
 
“Cleared out, far’s I can tell. Their booth and the tent back of it are entirely deserted. They’ll not be back, is my guess. Off on some big business. Pity is, we’ve missed their trail.”
 
* * * * * * * *
 
In the meantime, the lone pilot of the sky who had winged his way over Johnny’s booth an hour before was meeting with an unusual adventure. Had Johnny Thompson known who that pilot was he would have become excited beyond words, for this was none other than Curlie Carson. And Curlie Carson, as you will know, if you have read The Rope of Gold, had been Johnny’s companion in many wild adventures in that island of the Black Republic: Haiti. At the conclusion of those adventures they had parted. Now, with one of the queer tricks she appears to delight in, Fate had brought them within a very short distance of one another. And this time each was busy battling his way out from the tangle of mystery that was being woven about him.
 
25
After living in Haiti for a time, Curlie had found himself once more in the grip of wanderlust. Having returned to New York, he fell in with a friend who was in the Air Mail Service.
 
“Come with us,” his friend had invited. “Know the thrill of service in the clouds. Join a growing enterprise. Already Uncle Sam’s airplanes each day travel a distance equal to the airline that reaches from Chicago to Cape Town, Africa.”
 
Curlie had joined up gladly. A natural mechanic, and an aviator with several hundred miles to his credit, he was not long in gaining a place near the first rank of mail pilots.
 
When one of the regular Air Mail pilots flying from New York had been laid up by a case of nerves following a crackup, Curlie was given the stick. So here he was on his third long flight with fifteen hundred pounds of mail on board, his powerful plane drumming happily through the night.
 
26
Happily, but not for long. Scarcely had he passed over the bright lights that shone up from the “Greatest of all Carnivals,” than things began to happen.
 
The beginning seemed insignificant enough. His keen ears had detected a sound.
 
“What was that sound?” He had strained his ears in a vain endeavor to distinguish this new beat on his eardrums which had come to disturb him.
 
Not that there had been no sound before. There was plenty. For hours he had listened to the ceaseless roar of a six hundred horsepower airplane motor. True, this was muffled by a heavy radio head-set pressed lightly against his ears. But it was distinct enough for all that.
 
And now there had come a second sound. At first faint, indistinct. Then louder. Like bells, motors have their one definite sound and pitch. The experienced airman knows the sound of his own motor and many others.
 
“It’s a plane,” he told himself. “But at such a time, and such a place!”
 
27
Allowing one hand to rest gently on his control stick, he half rose in the cockpit to peer blindly into the void of darkness, of moonless night, that lay all about him.
 
For a full moment he remained standing thus, motionless, while his eyes swept in a circle, up, down and sideways, many times.
 
“No lights,” he murmured. “I take my oath to that. Dangerous business I’d say. Suppose they’d miss the sound of my motor, the gleam of my lights!” He shuddered at thought of a head-on collision, of broken wings, flaming planes and sudden death.
 
“Breaking the law, that’s what they are! Wish I had their number. I’d report them.”
 
Had he but known it, the occupants of this plane were infractors of the law in more ways than one. Not knowing, he settled back in his seat, gripped his stick firmly and gave his mind over to the important business of bringing the Air Mail from New York.
 
The drumming of the mysterious plane did not leave his ears undisturbed, nor did troubling thoughts pass from his mind.
 
28
“Up to something,” he told himself. He thought of one precious bit of cargo that lay so near him he might touch it with his feet.
 
“Forty thousand dollars,” he whispered. “Don’t seem that it could be worth that. But that’s what he said. And he’s always told the truth.”
 
“Snap on the radio,” he murmured after a moment. “May get some clue from that.” His plane was equipped with a receiving set by which weather reports and special orders reached him.
 
He was destined to receive a clue regarding the mystery plane, and that very soon. And such a clue! It would set his blood racing and his hands trembling.
 
But for the moment all was as it had been. Nothing came in over the air. His plane behaved beautifully. True, at times she bumped a bit as he speeded her up, but that was to be expected.
 
Half forgetting the other plane, he settled back in his seat to think of the hours that had just passed.
 
29
It had been George Wiseman, the mail clerk at the New York office, who had shown Curlie three unusual packages which went with hundreds of others to make up his fifteen hundred pounds of cargo.
 
Had Curlie been the usual type of air pilot he would have known nothing of those packages. He was far from the usual type. Instead of loafing about the hangar swapping stories with other pilots, he was uptown in New York, learning things.
 
His work and his mail interested him most. He was eager to know all about it from beginning to end.
 
George Wiseman had grown old in the mail service. He was tall, gray and stooped. His gray eyes were keen. He knew much and was willing to help the eager young pilot.
 
“You boys of the Air Mail know little enough about the service you perform,” he had said to Curlie as he busied himself with the tasks of making up the mail. “You see the mail in sacks. It’s packed away in the fusilage, and you go thundering away. At the other end it is dragged out, piled into a truck, and is away again.
 
30
“We at this end—” He reached for one of the registered mail pouches. “We know a little more, sometimes a great deal more. People confide in us. They tell us of their desires, their hopes, their fears.
 
“Take these three packages.” He jerked a thumb at a small, a medium sized and a rather large package. “To me they represent three things: a great necessity, an emergency and a mystery. To you—”
 
“Tell me about them!” Curlie had exclaimed quickly. “It will make the trip more interesting.”
 
“It will that!” exclaimed the aged mail clerk. “Even thrilling, you might say.
 
“That little one,” he went on, after ten seconds of silence, “is medicine, some sort of antitoxin, I think the man said. It’s for a very sick child, a beautiful little girl, five years old, a college professor’s daughter. She might die if you failed to go through.
 
31
“But there now!” he exclaimed. “Perhaps I’ve told you too much. It may bother you, make you unsteady.”
 
“It won’t,” said Curlie with assurance. “My mind doesn’t work that way. Been tried before. Added responsibility steadies me.”
 
“That’s the way to be. It’s the sign of a healthy mind in a healthy body. These boys that smoke a cigaret every four minutes, now. They’re not like that.”
 
“But tell me about that one.” Curlie pointed to the largest of the three packages.
 
“Worth forty thousand dollars.” The gray old clerk slid the package into the sack.
 
“Forty thous—”
 
“What the man said. Don’t doubt it. See who it’s for? Fritz Lieber. You know who that is.”
 
“The greatest living violinist.”
 
“Many say so. And this is his violin, one of them, perhaps his best.”
 
“But why here?” Curlie stared in astonishment.
 
32
“He has another. He likes the other as well; has it on tour. To-morrow in your city he is to play for fifteen hundred crippled children. That’s for the afternoon. At night he plays for the rich, the beautiful, the mighty, in the opera house. Thirty-five hundred of them. And his violin, his precious instrument, is out of commission. Don’t know why nor how. Somebody careless, probably.
 
“And this,” he added, placing a hand lightly on the package, “is his chance, the only other he can use.”
 
“His and the crippled children’s chance.” Curlie’s tone was almost reverent. “They shall have the chance. We’ll go through, my plane and I.”
 
Curlie recalled these words now as he ploughed on through the darkness and the night. Still there came to his ears the mysterious drumming of that other plane.
 
And then, suddenly, so loud that the speaker seemed at his very elbow, words broke in upon the thunder of the motor.
 
“The radio!” he whispered tensely.
 
“Official orders!” came in a gruff voice. “Land at once.”
 
33
“Land at once! in this darkness!” the boy thought in dismay. He was over a level farm country. The thing was possible. But why?
 
Emergencies, the child’s medicine, the violin, all called for full speed ahead.
 
“Land!” he cried aloud to the waiting night. “Land!”
 
There was no reply vouchsafed him. His machine carried no sending set.
 
“Land!” he muttered suddenly. “It’s a plot!”
 
He touched a lever. His motor thundered louder than ever and his thoughts raced with the plane.
 
“That,” he told himself a moment later, “was a mistake. It told them at once that I accept their challenge.”
 
But what did they want? Again his thoughts flew to the sack of registered mail in the fusilage just before him.
 
“Three precious packages,” he thought. “Can’t be the medicine. Who would rob a dying child?
 
34
“The violin! Forty thousand dollars! that’s it. They would rob the mail to get that.”
 
And yet, as he gave the matter a second thought, the thing seemed uncertain. There was no doubting the true value of the violin. But where would a robber sell it? Such instruments are few; they are known the world over. To offer a stolen one for sale would be to court arrest.
 
“There’s the third package,” he told himself. “Mr. Wiseman said this one contained a mystery. ‘A strange, wild-eyed man in shabby attire brought it to the office. He placed a twenty dollar gold piece on the counter, paid the highest possible insurance fee upon the package, which is heavily sealed with wax, and then without a word he walked away.’ Those were Mr. Wiseman’s very words.”
 
But now the time for reflection was past. The time for action had come. The voice was once more in his ear. Gruffer than before, it set aside all pretense.
 
“You’ll come down, or we’ll bring you down like a crippled wild goose!”
 
35
Curlie shuddered. What was this, a plain robbery, or did that mysterious package contain some terrible secret?
 
He was alone in the dark. The hour neared midnight. He was high in the air. What could he do?
 
“The mail bag is within my reach. I could swing out with it and jump. Parachute would save the treasure and me,” he thought.
 
But would it? The parachute was large and white. Even in the night it might be seen.
 
“Then they’d land and catch me. I’d crash my plane for nothing, and all that mail would probably be burned.”
 
Crash the plane! No. He couldn’t do that. That old plane meant much to him. In it he had outridden many a wild storm.
 
Then, too, there was the Air Mail pilots’ slogan: “The mail must go through.”
 
“And it shall!” he shouted into the night.
 
“You’ll come down!” the voice from the air insisted.
 
In his desperation the boy lifted his eyes to the skies in silent prayer.
 
36
Did the answer come at once? Be that as it may, a thought flashed into his mind.
 
In the fusilage directly behind him was a twelve foot parachute. Fastened to the parachute was, of all things, a large doll and a new doll buggy.
 
On the route, a few miles beyond a small city, was a farm. Curlie had made a forced landing there the trip before this one. There he had made the acquaintance of a child, a happy, most cheerful little girl, and yet a terrible cripple.
 
Curlie read his Bible. He believed what he read. Some day, if he fed the poor, visited the sick and was kind to crippled children, he would hear the great Master say, “Come!”
 
He had written a letter to the crippled child, had received an answer and had learned that she wanted a doll and a doll carriage. This day he had meant to send the gifts down by a red parachute. The clouds had hid the little farm. The parachute was still behind him.
 
37
“If I remove the doll and attach the registered sack to the parachute I can toss it over and they won’t see it. Red shows black at night. They’d never find it. Then I can land and take what comes.”
 
“You have two minutes to land!” The voice was more threatening than ever.
 
Two minutes! The hum of the other motor grew louder. The radio was not on that plane, but on some building not so far away.
 
Two minutes! He worked feverishly. The cord stuck. He cut it, then tied it again. He dragged out the bag. He lifted the parachute free.
 
“The violin!” His heart sank. Yet the parachute would lower the sack gently to the ground.
 
“It’s the only chance.” With one wide, clear swing, he tossed the sack over.
 
The next instant his plane tilted downward. Not a moment too soon, for a motor thundering by passed again into the darkness.
 
“Meant to shoot me down,” he muttered breathlessly.
 
He reached for a switch, pulled it, and at once saw a finger of light from his powerful landing lamp pointing earthward.
 
38
For a space of ten seconds he studied the surface of the ground.
 
“Level pasture. Take a chance. Land in the dark. Might escape.”
 
Again there was darkness. And now, too, came silence. He had shut off his motor.
 
“They’re landing, too,” he thought with a thrill and a shudder. “I wonder where?”