Through the door came a muffled hail.

“Hello, inside the boathouse!”

According to a plan already made Don tiptoed into a dark corner as Garry went swiftly, silently, to the other, nearest the land side of the old building.

Chick, smallest, quickest of the three, crouched close beside the closed door, pressed tightly against the wall.

A hand fumbled at the latch. The door swung sharply inward. A beam of light leaped across the enclosed space. Instantly Chick lunged forward: his arms wrapped about a pair of slim legs.

“I’ve got him!”

As the man toppled forward Garry and Don came like panthers from the respective corners, springing on the figure. Realizing his helplessness their antagonist grunted a surrender.

Don kicked the door shut. Garry saw that his comrade placed his back against it, and let go his hold. Chick sprang back, tense and ready for any surprise move.

“Just as I thought,” Don said triumphantly. “The air mail flyer!”

“And what of it?” The man got to his feet, as Garry picked up the electric flash and laid it on the table, still glowing.

He directed its beams on a quantity of objects they had set there, ready for such a climax.

“We’ll tell you,” Don began. “First, Mister Pilot, you learned from the Indian, John, that there was some treasure hidden somewhere in this swamp. You went to the Indian village, concealing most of yourself in your pilot’s togs. Then you located the map Ti-O-Ga had, and took a picture of it with a vest pocket camera, came back and used our dark room enlarging outfit to make the tiny picture big enough to trace out and then you camouflaged that map tracing with wings and other airplane parts.”

Garry turned his light on various objects as he took up the accusation.

“This is the vest pocket camera.” He brought it into sharp relief. “Chick found it in your cottage room.”

“You’re crazy! I never owned one.”

“No use blustering!” Chick cried. “The whole thing is plain to us! You wanted a bigger map so you could lay out cross-sectional lines on it and number them. I made a blue-print of the tracing while we had it and by good luck I had picked up two pieces of paper to print on, and then put one aside, the lower one; but it was clear enough, after we made a contact negative from it on film, and then redeveloped and intensified that! We saw the cross lines, and the figures on the paper checked with figures on the bottom of the tracing, most of them being checked with pencil checks to show they had been covered.”

“And what did I do that for?”

“You laid out a chart of this swamp over the camouflaged map,” Don took up the accusing story, “then you went to Port Washington and bought an amateur movie camera, and a lot of film. Garry knows the photography store owner, and he got his home, tonight, and learned that a man in pilot’s togs who said he was a mail pilot, bought the outfit.”

The man was impressed. “Clever, but not true!” he scoffed.

“All through the mystery,” Chick cried, “you have been camouflaging! You covered your trail by putting suspicion on others. That tracing, in this place, puts suspicion on the theatre man, Toby Tew, because he was one who’d know how to do the ghost trick with an old airplane crash film and a projector.”

“You put the key to the locker where you hid the projector you used at the hangars, late at night, in the control chief’s vest, because he might have been able to cast airplane shadows on clouds with the searchlight beam!” Don spoke crisply, “and—you camouflaged the map—but, then, you overdid it!”

“Yes!” agreed Garry, “you went too far. You wanted to make the tracing seem like a new design, after you saw the control chief’s initials on the tracing he left here! So you drew in on the entering-edge of the wing’s a ‘slotted-wing’ sketch. Now, the control chief knows light, but he doesn’t know that a slotted wing is an invention that helps to reduce ‘burbling’ in take-off, and lets the ‘camber’ of a wing change automatically—that’s too technical for a control man. Only a pilot would know that, because it’s patented and controlled by one English firm.”

“And your camouflage showed us that the man we wanted must be a pilot, just by that!” cried Don. “Then we examined the frame-bracing and saw the little cross-mark you had to show where the map said to look for buried treasure—only you were looking for a ship!”

“All very cleverly worked out—but you’ve got the wrong man!”

“We’ll see! Chick, set off the red, white, and blue signal to the Chief,” Garry ordered. Chick’s move toward the door was arrested by a startling sound under the flooring. They all stood petrified.

Slowly they wheeled to watch the trap in the corner. It opened. Up came the green-capped, green-masked head, the oilskin shrouded body and rubber-gloved hands of their Demon—the Man Who Never Lived.

“Gosh-a-mighty!” he croaked hoarsely, “but you’re bright boys!”

“Toby Tew!” Chick exclaimed, recognizing the phrase. “You!——”

“In the name of all-possessed!” croaked the figure, “who else?”

“You’ve got your ‘nerve’ to brazen it out this way!” Garry said; but there was a strange look on his face; the voice, for all its disguising hoarseness, seemed oddly familiar—and not that of Toby. “Are you just doing it to try and save this mail flyer?”

“Gosh-a-mighty!” the figure retorted, “no! Time’s passed for trying to camouflage, that’s all. You think you read that traced chart? You didn’t! That cross telling where treasure was hid, now! I put it on the tracing to keep you away from the real spot, same as I bought an old, discarded skeleton from a hospital and had it discovered to start people looking in that locality—far away from where I dug and scooped in mud.”

“Well,” Chick cried, “you are caught! The swamp is watched. When you left the Chief, he had you watched.”

“Gosh-a-mighty! No such thing! He left us all go. All I had to do was to go home, start to go to bed, get these togs, walk down to the seaplane landing stage, tell the detective on guard I was a special officer assigned by the Chief to patrol the swamp shore—then in I got in that crash boat—and here I am, with good tail-winds and everything my own way!”

“You’re not Toby Tew!” Garry exclaimed.

“Toby doesn’t talk about ‘seaplane landing stages’ and ‘tail winds.’ Those are aviation and he’s a boatman as well as a theatre man—and he can’t fly!”

“Then it’s Doc!” cried Chick.

“No!” Don had caught the expressions and rightly judged them. “Doc couldn’t draw an airplane tracing: certainly the only other man besides this mail flyer, who knows about slotted wings and can make them is——”

“Scott!”

As Garry shouted it the disguised man nodded.

“But—Scott flew us here at the first,” Chick expostulated. “Besides—he’s injured!”

“Camouflage!” laughed the man, brazen and triumphant. “I got you to fly here to make sure you wouldn’t suspect me. Besides, it helped me get the ship here, so I could go in a dory to my helicopter, and ‘put on my sky show.’ Then—with the storm coming, I had the Dart to get back in: I used these oilskins, while I dug. I had the tracing made to guide my aerial photography, and as soon as I located the buried chest I left the tracing where it would get Doc suspected. I left a key where it might incriminate the control chief. The more people you suspected the more I could work. I had to burrow for that treasure—but—now—I’ve got it all loaded and ready to fly to a place where a boat can take me out to the twelve mile limit. There a rum-runner will ship me for parts unknown. As far as being hurt by the ‘prop’ goes, I pretended that to get out of flying that night—I knew the Indians were after me. And now——”

“You can’t escape!” taunted Chick. “The swamp is surrounded.”

“But the police left some very powerful arguments where I could get them—and they’ll help me escape instead of catching me.”

Then the figure on the ladder snatched a round, queer object from under its oilskins.

Instantly the reference to police supplies became clear to Don.

“Look out!” yelled Don. “Tear-gas—don’t breathe—run!”

The bomb flew, dropped, burst. Garry and Chick, their sleeves held over their faces, leaped toward the doorway; but the bomb, flung at Don’s feet spread its fumes swiftly. The trap door slammed to the roar of exultant laughter.

The pilot, off guard, stumbled against the table and fell. There came a cry and a cough—and silence. Choked, gasping, with smarting eyes streaming with tears, the chums staggered out.

“In case you might wonder—” Scott’s voice floated to them from the humming electric launch, “I left the hospital the same night I pretended to be injured by the propeller—I knew the Indian was going to try to drive me down, and pretended to be laid up. But I could run fast enough to come back, smoke you out and get the film—it had a picture on it I didn’t want seen—and I flung it out into the swamp and went back to my room—put the things that you found in that mail flyer’s room where you saw them—and came back to stay with the Chief till he sent me off to bed—only, I came here to load the treasure. Now—good-bye. It flies in five minutes!”

“Not much it doesn’t!” muttering, choking, coughing, Don gasped orders. Flares to signal, as soon as Chick and Garry got the pilot out of the house. His job was to start the Dragonfly. He staggered to the wharf-side, dropped into the craft—saw that the ignition wire was cut!