"You can't really judge distances in air accurately. There are powerful equipments which might be mounted on either automobiles or airplanes."

"The thing that puzzled me, though, was his line of chatter. All about some 'map, old French,' and a lot of stuff like that. I—"

Suddenly he broke off. A grinding sound had come from one of the loud speakers. There followed in a clear, strong voice:

"Map O.K. Old French is amazing. Good for a million."

Curlie's fingers were busy once more as a tense look drew his forehead into a scowl.

"About fifteen miles," he whispered.

Then the voice resumed:

"Time up the bird. When?"

A tense silence ensued. Then, faint, as if from far away, yet very distinctly there came the single word:

"Wednesday." This was followed by three letters distinctly pronounced: "L.C.W."

A second later came the strong voice in answer: "A.C.S."

"That," said Curlie as he settled back in his chair, "in my estimation ends the night's entertainment. But the nerve of the fellow!" he exploded. "Sending that kind of rot on six hundred. Why, at this very moment some disabled ship might be struggling in a storm on the Great Lakes or even on the Atlantic, and this jumble of words would muddle up their message so its meaning would be lost and the ship with it. The worst I could wish for such a fellow is that he be dropped into the sea with some means of keeping afloat but with neither food nor drink and a ship nowhere in sight."

If Curlie had known how exactly this wish was to be granted in the days that were to come, he might have experienced some strange sensations.

He straightened up and placed a dot on the map before him.

"That's where he was. I'll motor out in the morning and have a look at things. May discover some clew."

Curlie was a bright American boy of the very best type. Like most American boys who do not have riches thrust upon them, when he wanted a thing he made it or made a way to get it. Three years previous he had wanted an automobile—wanted it awfully. And his total capital had been $49.63. He had been wanting that car for some time when an express train hit a powerful roadster on a crossing near his home.

Having flocked in with the throng to view the twisted remains of the car, he had been struck with an idea. This idea he had put into action. The railroad had settled with the owner for the car. They had the wreck of it on their hands. Curlie bought it for twenty-five dollars.

To his great delight he had found the powerful motor practically uninjured. The driving gear too, with the exception of one cog wheel, was in workable order. The remainder of the car he sold to a junk dealer for five dollars. It was twisted and broken beyond redemption.

He had next searched about for a discarded chassis on which to mount his gears and motor. This search rewarded, he had proceeded to assemble his car. And one fine day he sailed out upon the street with the "Humming Bird," as he had named her.

"Better call her 'Gravel Car,'" Joe had said when he saw that she had no body at all and that he must ride with his feet thrust straight out before him in a homemade seat bolted to a buckboard-like platform.

But when, on a level stretch of road, Curlie had "let her out," Joe had at once acquired an immense respect for the Humming Bird. "For," he said later, "she can hum and she can go like a streak of light, and that's about all any humming bird can do."

No further messages of importance having drifted in to him from the outer air, Curlie, an hour before dinner, made his way down to the street and, having warmed up the Humming Bird's motor, muttered as he sprang into the seat: "I'll just run out there and see what I see."

A half hour later, just as the first gray streak of dawn was appearing, he curved off onto a gravel road. Here he threw his car over to one side and, switching on a flashlight, steered with one hand while he bent over the side to examine the left-hand track.

There had been a light rain at ten that night. Since that time a heavy car with diamond-tread tires had passed along the road, leaving its tracks in certain soft, sandy spots.

"Maybe that's him," Curlie murmured.

A little farther on, stopping his machine, he got out and walked along the road. Examining the surface closely, he walked on for five rods, then wheeled about and made his way back to the car.

"He was over this road three times last night. That looks like a warm scent. Can't tell, though. My friend might not have been in a car at all; might have been in a plane.

"We'll have a look at the very spot." He twirled the wheel and was away.

A half mile farther down the road, he paused to look at a map. "Not quite here," he murmured. "About a quarter mile farther."

The car crept over another quarter of a mile. When he again came to a halt he found himself on a stretch of paved road. "This is the spot from which the last message was sent. Tough luck!" he muttered. "Can't tell a thing here."

Glancing to his right, he sat up with a start. He had suddenly become aware of the fact that he was just before the gate of the estate of J. Anson Ardmore, reputed to be the richest man of the city.

"Huh!" Curlie grunted. "Car must have stood about here when that last message was sent. Maybe it went up that lane. Maybe it didn't, too. J. Anson's got a son, about my age I guess. Vincent they call him. He might be up to something. There's a girl, too, sixteen or so. Can't tell what these rich folks will do."

He stepped down the rich man's private drive, but here the surface of crushed stone was so perfectly kept that no telltale mark was to be seen.

He did not venture far, as he had no relish for being caught trespassing on such an estate without some good explanation for his conduct. Just at that moment he had no desire to explain.

As he turned to go back, he caught the thud-thud of hoof beats along the private drive.

Fortunately the abundant shrubbery hid him from view. Hardly had he reached the machine and assumed the attitude of one hunting trouble in his engine when a girl rounded a corner at full gallop.

Dressed in full riding costume and mounted on a blooded horse, she swung along as graceful as a lark. As she came into the public highway she flashed Curlie a look and a smile. Then she was gone.

Curlie liked the smile even if it did come from one of the "four hundred."

"Gee! Old Humming Bird," he exclaimed as he patted his car, "did she mean that smile for you or for me? So there might be a girl in the case, same as there seems to be in that one over at the hotel? Girl in most every case. What if she sent those messages and I found her out? That would sure be tough.

"But business is business!" He set his mouth grimly. "You can't fool with old Uncle Sam, not when you're endangering the lives of some of his bravest sons at sea."

He threw in the clutch and drove slowly along the road. Twice he paused to examine the tracks made the night before. Each time he discovered marks of the diamond tread.

"That radiophone was mounted on a car," he decided; "I'll stake my life on that. Now if he keeps it up, how am I to catch him?"

The next night found Curlie in the secret tower room alone. Joe Marion was away helping to run down a case of "malicious