After a somewhat disappointed study of the three yellow picture theatre passes, Garry turned to the Indian youth.

“John,” asked Garry, “what do these mean? There isn’t anything on them but printing. They say, ‘Admit bearer’ and give the Palace name and they are signed by the theatre manager. But there isn’t any help there, unless something is written on the backs in disappearing ink.”

“Maybe, if we heated them, or wet them, something would come out,” suggested Chick hopefully, “as they stand, they are just three passes.”

John, with a quiet smile on his copper-colored face, replied curtly:

“My father is a clever man. He put this with that, and know much. You try doing that.”

“Personally,” Mr. McLeod was a trifle sceptical, “I think they are part of the plot to confuse you and the rest of us. No doubt the old ‘medicine man’ is clever—clever enough to be involved in some way and to try to pretend that he is a helpful chap when his whole attention is to throw out a smoke screen to protect himself and—” he frowned at the young Indian, “—his son.”

Garry put them back in the skin bag, slipped it into his pocket and switched in the current to back the launch around.

“You might try using those passes,” the control chief suggested, as the boat moved down the channel.

Garry nodded.

“We will,” he agreed.

With the ignition key and a carburetor needle and float removed, the helicopter, tied once more to its stakes, was in no danger of being removed. They felt that they could safely leave it: no one would be able to use it with parts so vital missing. If the owner had a spare switch key, it was totally unlikely that the carburetor parts were duplicated.

Don’s plan, quietly communicated to his two friends and to Mr. McLeod, was to be tried.

They would leave the disabled helicopter as it was, go back to their daily tasks in the designing department of the aircraft plant and the airport, and keep a watch on the control chief, on Doc Morgan, and on the swamp, from the control tower balcony, with strong binoculars.

No garage, accessory store or hardware shop could replace the special carburetor parts for some time; after instructing their own shop foreman to report any application for the parts that might be made to him, Don rode in to Port Washington with his uncle and visited every shop, garage and other place where such things were available, told enough to enlist attention, without disclosing any of their suspicions about the tracing and its possible meaning, and secured a promise to have a report made of any request for carburetor floats and valves of the unusual type they had looked up in the catalogues.

“Now,” remarked Don, as their sedan returned to the airport, “if any spook, or man who calls himself a thing that never was, comes around to put his helicopter into commission, we can grab him, for we will know that no one else would be after floats like the one we removed.”

His uncle nodded, morose and uncommunicative.

Rejoining his chums, Don explained his recent activities.

“I found that the blue-print files had the lock picked,” Chick told him, “and the blue-print I made of the sketch was gone.”

“I’ve just come down from the tower balcony,” added Garry. “The helicopter hasn’t moved. I just barely made out the blades above the grass. The way they are kept when it isn’t being used, the blades are sideways to the line of sight from the control tower. That’s why none of us, especially since we weren’t looking for it, ever saw the thing.”

“Probably Mister Spectre-Man had it there all during the haunting time,” Chick remarked.

“But what did he use it for—and how did he use it?” objected Don. “The spooky airplanes were biplanes, old-timers, and there never was a helicopter in sight.”

“I suppose he used it to get to his other ships, and then flew them between a cloud and a light, so the shadows appeared, just as the shadow of your Dart showed to us the first night we tried being Airlane Guards,” Garry suggested.

“But why should he hide it in the swamp, and need it at all? If he had a biplane, he could take-off from miles away,” Chick argued.

“It’s as much of a puzzle as that mixed-up affair of a chart that may be an airplane design, or a camouflaged drawing of a privateer or old-fashioned brigantine that has treasure hidden in it,” Chick mused. “Now, we’d better get to our watching. Doc is my assignment. He’s eating breakfast, so I’ll go and get some, too.”

“Control Chief Vance has gone to bed,” Garry said. “I won’t have very hard work keeping track of the cottage he lives in, from the platform where I watch the helicopter. Don, you’ll be free, then.”

“Well, I’ll work on the inking in of the new tracings,” the young pilot decided. “Wouldn’t it be odd if my study of airplane design had some good effect in clearing up our mysteries?”

“It certainly would!” agreed Chick, moving away.

While he used square and compass, drawing pen and India ink, making the perfect outlines and shading on tracing paper which perfected the multitude of parts’ designs, before the working blue-prints were made by Chick and Garry, Don kept that idea in the back of his head.

It would be fine, he mused, to be able to use the knowledge he had gained, especially about airplane construction and the creation of the original plans for new models, to solve the puzzling, baffling set of unexplained circumstances.

The possibility seemed far-fetched, though.

“How can it help that I know about streamlining the body, and the struts, and even the flying wires?” he asked himself, “or what can I make of wing-taper, and camber, and all that?”

He completed the application of India ink to the drawing of a seaplane body, in outline, showing the many braces and their points of attachment to the longitudinal “keel.”

He put it away, with others, in a folder when it was dry.

“I guess knowing about designs won’t help, any more than knowing how to fly a ship was of any use to the Airlane Guard,” he murmured, laying the folder aside for Garry’s later use.

“If we only had the ‘ignition key’ so we could make ‘contact,’” he smiled at his application of aviation terms to their puzzle, “it would be easy to give it the gun and fly a straight course to the solutions.”

When dusk came on and the chums gathered to compare notes, the day proved to have yielded blanks all around.

“The Indian told the truth,” Garry reported. “Your uncle has engaged a private detective and he checked up. John and old Ti-O-Ga are ‘playing a split week’ engagement at the Palace, starting Saturday—today. The helicopter hasn’t been moved. A private detective is there, watching it, and one is in the hangars.”

“We can go to the movies, then,” suggested Don. “Let’s see if the old ‘medicine man’ meant anything by giving us passes, and telling us to take them out of the bag after seven days.”

“He might, at that,” Garry became more animated. “That connects up, because after seven days he knew he would be here, with his son.”

“I hadn’t seen it that way,” responded Don. “Let’s go!”

They found the Palace, on a side street, fairly filled when they presented the three yellow slips to the door man. Large “cut-out” figures of Indians, in various poses, and posters, from “one-sheets” to “flash twenty-four sheets,” decorated the theatre and billboards nearby, showing in blatant coloring the scenes from “Red Blood and Blue.”

The doorman, to whom the chums were well and favorably known, chuckled as he accepted the “dead-head” tickets.

“Papering the house, eh!” he chaffed, referring to the method by which, issuing free tickets, a manager sometimes made it appear that his theatre was well patronized. “Well, you won’t like the show.”

“Why?” Chick demanded.

“It’s the old story that the fellow who comes in free does all the ‘knocking,’” responded the doorman, “I ought not to let you in at all, by rights. Passes aren’t good on busy week-end nights; but these are good any time—specials from the boss. How’d you get them?”

“In the most ‘charming’ way you could think of,” Garry made a hidden reference to the Indian’s “magic bag.” “They were ‘gave’ to us.”

“All right. Go on!”

In they went, finding a trio of seats about the center of the small and rather old-fashioned theatre.

A comedy was just reaching its end, and the jet silhouettes of a fantastic kitten, gyrating across the screen from a kick, punctuated their arrival with a gale of laughter from the audience.

They were just in time for the “presentation,” preceding the main attraction.

The heavy draperies of the softly lighted curtain swung down, concealing the stage until the screen was taken away.

Softly the small orchestra began a weird musical number, while from the projectors that threw the pictures onto the screen, their lenses showing colored lights instead through tinted isinglass disks, came a combined rose and blue that gave the stage, as the curtains opened, the effect of dusk coming on just after sunset.

Weird tom-toms thudded gently from the enclosure which pictured a forest background. Before this, around a small “practical” fire, well protected, sat some supers, made up as Indians.

“There’s John Ti,” murmured Chick to Garry.

“He’s going to sing!”

As Garry spoke the young Indian broke into a chant, with a melodious voice, standing against the soft light supposed to be the dying sun’s afterglow over the sea, to one side of the stage.

Three white people came into the scene, watching, all evidently campers, from their dress. They were extremely modern, both in pantomimic actions and in their garments. One was a girl, the other two were men, and their attentions to the girl spoke clearly of great interest in her.

To the increasing rapidity of the music after the song, those make-believe warriors seemed to be caught by the spirit of some old mood, and they rose, moving about, presenting a colorful, barbaric picture as they began a dance, to the thrum of the piano and the song of violins, while dull drumbeats punctuated the music.

From the wings, as the music became more wild, appeared the old Indian in blanket, feathered head-dress and other marks of his chieftainship.

One of the men began to make motions calculated to show his feeling of superiority toward the stalking old man, and the girl turned from him in a sort of distress, then the other man caught her hand, whereupon his rival glowered, and his hand moved toward his hip.

At once the old chief stretched out an arm—the dancers drew back and squatted, the chief approached the fire, beckoning to the girl.

She approached slowly, fearfully, and the music became low as the chief, squatting, drew out a bag, extracted from it some herbs which he threw into the fire.

At once a great pillar of whitish, dense smoke rose, straight upward toward the wings.

“Clever, isn’t it?” whispered Garry. “They must have a fan under the trapdoor of the stage, just below that fire, to make those flames leap and the smoke go straight up.”

“It makes me feel sort of creepy, and as if it was real!” Chick responded. Then they watched, in surprise.

In that white, thick, ascending pillar of smoke, as though on a screen, there slowly appeared a vision!

There was the girl. There were two men. But they were Indians.

A quick pantomime in the moiling, upcurling smudge revealed hatred between the men, and fury when the girl chose the rival.

Into that vision blended another so that as one vanished the other was visible. It showed the two men, again with the girl, but as they actually stood on the stage, almost the same in appearance, as near as the men engaged by the theatre could be matched to the vision.

That picture of hatred was again enacted in the new garb, and the vision was once more displaced by another—and the chums gasped.

In that smoke column, black against white, two biplanes flew one after the other toward the audience—they seemed to merge, to blend, to vanish, and then—as Chick made an involuntary little scream of amazement—the smoke was filled by the vision of two black, bi-winged shapes coming together.

The drone of their arrival filled the theatre: so realistic was the effect that the planned scream of the girl on the stage was echoed by women among the watchers—to the rumble and roar was added the culminating contact.

The vision died as the translucent screen through which it had all been observed was gradually lighted by the first scenes of the real picture, showing the events of the story which began at the crash.

“Well!” muttered Don, “did you see what I saw?”

“The very same as the spectre in the cloud!” agreed Garry.

“Yes,” Chick contributed, “and I see the clue in the smoke, fellows. Every time that spook has appeared—it has been a cloudy night!”

“That’s it!” Don agreed. “The cloud acted as a screen—and now we know what was done—a picture was thrown on a cloud. But how—and by whom?” He paused. The theatre manager, passing up the aisle, gave them a pleasant salute—and all three mentally answered Don’s query!