seated themselves beside him.

“Fire away,” said Jack.

“What would you say to my finding the tracks of a peg-legged man coming up out of the sea, crossing the sands of Starfish Cove and disappearing into the trees beyond there?”

The inlet which Bob thus referred to was some three miles distant, with a patch of timber some twenty yards back from the water and a ring of low sandhills behind the woods.

“A peg-legged man?” said Frank. “That certainly sounds piratical. Go on. Your imagination is working well to-day.”

“Did he arrive in a boat?” asked Jack.

Bob nodded.

“Yes. I found where the boat had been run up on the sand. But—he didn’t leave. The boat went away without him. He disappeared inland, and there were no tracks marking his return.” 9

Jack whistled.

“Whew. Did you follow?”

“Did I follow? Huh. You can just bet I did follow. And, say, fellows––”

“What?”

“I know now where that strange interference in our radio receivers comes from.”

“Is that so?” demanded Jack, excitedly. “It was cutting up didoes just a few minutes ago, just before you arrived. Had been for some time, too.”

“Well,” said Bob, “that’s not to be wondered at. For when I followed Peg Leg’s tracks through the trees I discovered a radio station tucked away in a hollow behind the timber, with sandhills hiding it on the landward side. I watched for a while from behind a tree, but couldn’t see anybody. Then I hustled here to tell you fellows about it.”

Puzzled, the trio regarded each other in silence. Presently Jack spoke.

“Look here, fellows. There’s something queer about this. A mysterious radio station, hidden away, that sends a continuous wave on a hitherto unused wave length. This has been going on for a week. What does it mean? Then there is this man, this Peg Leg, whom Bob discovers arriving from the sea.”

“Let’s go together and investigate,” cried Frank, jumping to his feet. 10

“I’m with you,” declared Bob, also arising. “I would have gone up to the station and done that very thing, by myself, but—I don’t know—there was something about it all—something sinister.”

“Wait a minute, you fellows,” said Jack, also springing upright. “We can’t go putting our heads into trouble recklessly. Bob’s good sense prompted him when he refrained from pushing up to that radio station by himself. There is something sinister about this. That place is isolated, there are no roads near it, nobody ever hikes along that beach except us. How did the station ever come to be built? Why, the material and supplies must have been brought by boat. They couldn’t have been transported overland very well.”

“What shall we do, though, Jack?” asked Frank, impatiently. “You can’t reasonably expect to have a thing like this rubbed under our noses without our going ahead and investigating.”

There was so much plaintiveness in his voice, as of a child from whom a toy was being withheld, that Bob and Jack both burst into laughter. Then Jack sobered.

“Tell you what I think,” he said. “It’s only mid-afternoon. Let’s get out your plane, and take a look at this place from the air.”

“I guess the old boat is working all right now,” 11 said Frank. “How about it, Bob? You know we haven’t been up for two or three weeks, Jack. Bob’s been tinkering with it. When I last saw him at work, he seemed to have the engine entirely dismantled. Looked to me as if he had enough parts for three planes. Did you get it together again, Bob?”

“Yes,” said Bob. “And she’ll fly now, boy, believe me. Well, come on,” he added, starting for the hangar, not far distant but out of sight behind the sandhills.

The others followed.

From the Hampton radio station to the hangar on the Temple estate where Frank and Bob kept their plane was a short jaunt, and the ground soon was covered. Then Bob unlocked the big double doors and rolled them back, and the three trundled the plane out to the skidway where Jack spun the propeller while Bob manipulated the controls. As the machine got under way, Jack ran alongside and was helped in by Frank.

Out over the sandy landing field trundled the plane rising so quickly that Bob nodded with satisfaction. The loving work he had put in on the machine had not been wasted. It was in fine flying condition.

They were not far from the coast and in a very short time were flying over the water, whereupon Bob made a sweep to the right and the plane headed westward. The Atlantic rocked gently below, serene under a smiling sun and with only the merest whisper of a breeze caressing it. On the southern horizon 13 a plume or two of smoke, only faintly discernible, marked where great liners were standing in for the distant metropolis. To the north, far away, showed a sail or two, of fishing craft or coastwise schooner.

An exclamation escaped Frank and he leaned sidewise, gripping Jack by the arm and pointing with his free hand. But Jack had a radio receiver clamped on his head and was frowning. He glanced only hastily in the direction indicated by Frank, then shut his eyes as if in an effort at concentration.

Frank continued to gaze, then bent down and unlashed a pair of binoculars from a pocket in the pit and, putting the glasses to his eyes, threw back his head and began scanning the sky. After staring long minutes, he hastily put aside the glasses, lifted the radio transmitter strapped to his chest and spoke in it to Bob:

“Bob, there’s a plane overhead. So high you can’t see it with the naked eye. But I spotted it before it rose too high, and followed it with the glasses. The fellow’s up where the sun plays tricks with your eyesight. And, Bob, I’ve got a hunch he’s watching us. There’s Starfish Cove below us now. Keep right on flying. Don’t turn inland.”

Bob nodded, and the plane continued its way westward offshore. Frank again took up the glasses and searched the sky, gradually increasing the focal 14 radius. An exclamation from Frank and a hurried request in the transmitter presently reached Bob’s ears:

“Shut her off, Bob, and let’s land on the water. Quick. I’ll explain in a minute.”

Obediently, big Bob shut off the engine, and the plane coasted on a long slant to a safe landing some hundreds of yards out from the sandy, deserted shore.

Bob and Jack snatched the headpieces off, and turned inquiringly to their chum.

“Here,” cried Frank, pressing the glasses into Bob’s hands. “Take a look. That plane is landing way back there, and I believe it is at Starfish Cove.”

Bob was too late to see if the situation was as Frank described, however. Putting up the glasses, he turned to his chum.

“Tell us about it,” he said.

“Yes,” said Jack. “I heard what you told Bob, but not having the glasses I couldn’t see. At first, when you punched me, besides, I was thinking over that business of the strange interference with our radio and wondering what it could be. So I didn’t get to see. I suppose you were trying to point out this other plane to me then?”

Frank nodded.

“Yes,” he said, “it was just a tiny speck at that 15 time, but I could see it with the naked eye. However, it disappeared immediately afterwards.”

“Well, what made you believe the other plane was watching us?”