Smelling still of the fumes from the smoke flare, which someone—Doc Morgan probably—had cleared out, the dark room was close and unpleasant as Chick closed its door and, switching on the white printing lamp, faced his two friends.

“Let’s be very quiet,” he said, earnestly. “I was only half listening to the arguments. While they went on I thought of a way to draw the real ‘Ghost of Mystery Airport’ into the open—or—into the darkroom!”

“I don’t understand,” Garry spoke softly, although the door was tight.

“You mean by showing what we had clipped out of the film?” Don asked. “It was just put in the fixing bath—how do you know the fumes of the chemicals in the smoke bomb didn’t ruin it—stain it or fog it?”

“I don’t care a whack of a stick about the clippings,” Chick stated. “This is my plan. When I was in here before, I put the bits of film in the wash water, but they were all dirt, and chemicals. I don’t believe they’re worth bothering with. But—I know that the ‘ghost’ is among the people in the designing room. Doc followed Toby. Mr. Tew volunteered to come and listen. The air mail pilot was loitering around, listening. The two Indians——”

“Oh, I’m sure it’s one or the other,” Garry agreed, “but that doesn’t tell us your plan or how we can see which one it is. For my part, I’m in favor of looking at the film clippings. If they show us that we have the right idea, that a flyer has been taking pictures over the swamp, it will prove he is looking for the treasure, and not just trying to ruin Don’s uncle——”

“Oh, we know the motive—treasure hunting,” Chick retorted. “That’s been our trouble, before. We’ve tired so hard to show what was being done, and how, that we couldn’t take time and brains to discover—who!”

Garry was a trifle nettled.

“I suppose you are going to discover ‘who’ without even looking at the clue Scott thought might be in that undeveloped film.”

“I’m going to make him—discover himself!” Even Don stared.

Garry laughed, a little scoffingly.

“All right!” Chick took the implied unbelief good-humoredly. “Think this over: If you had flung a smoke bomb, and gotten away with evidence, and you heard somebody say they had some already developed—what would you do?”

“Run!” chuckled Garry.

“I wouldn’t!” Don saw Chick’s argument.

“I’d be uneasy, and uncertain, and I’d worry until, finally, I might feel compelled to come and see just how much you had against me!”

“That’s my plan!” retorted Chick.

Garry agreed with Don. It was clever of the youngest chum.

“While we wait, we might as well see if we have evidence, or whatever it may be—against anybody!” Don added.

Chick lifted the wet film from its washing bath, handling it carefully by the edges to avoid spoiling the wet, swollen, delicate surface emulsion containing the pictures.

Holding it up to the light, he showed a smoky, already somewhat distorted image in one piece of the clipped film.

“I can see—letters,” Don said, peering toward the light. “There’s an ‘A’ followed by a figure ‘one’ and then—it’s spoiled by scraping on the floor when the fixing trap got upset.”

“Just on the edge of the last ‘frame’ of moving picture film, you can see a flat, opaque blur,” Garry commented. “That’s an aerial picture, taken from above! I’ve seen those air photographs in the movies. What’s to prove this is a picture of our swamp? It’s all fogged!”

“I count more on our ‘ghost’ coming here than on that film,” Chick declared. “I’ll put that in a drying clip, and hang it behind the tanks in case we can use it sometime. Now, here’s the other clipping!”

The second one he exhibited was more clear.

“That’s the swamp, all right,” Garry commented. “The first one is one of the smoked-up parts we threw away after the first trial. But this one is the swamp, and no mistake. That is,” he corrected himself, “it’s a section of it, along the water front. See how the shore curves in and out—and the beginnings of Crab Channel and the other smaller inlets?”

Chick and Don assented; but the pictures gave them nothing new to go by, more than assurance that somebody had flown over the swamps to take air films. Of course, as Chick argued, that fitted in with the idea that the mysterious “somebody” had put the projector head and the other things into a locker of the pilots’ quarters as a means to throwing suspicion on another, as the key in the control chief’s old coat and vest proved. The film with it was not the same as that used for the apparition in the cloud. It was only a “blind,” as Chick argued.

Also, as Don added, the film could have been taken by the control chief as well as by another, except that he was seldom away daytimes.

“But Doc Morgan is,” Garry remarked. “And Toby Tew is in and around the swamps all Summer, and could easily hire some pilot from another airport to fly him—nobody would have paid much attention, because the engineers were using airplanes, too. And I think it was to stop the engineers from draining the swamp before he had taken the treasure that our ‘ghost’ worked his spectre-in-the-clouds!” he added.

“Sh-h-h-h!” Chick caught each by an arm. “Listen!”

Footsteps sounded on the floor outside, approaching. Were they hesitating? Did they echo with such caution because they belonged to a guilty body? Slowly they came closer.

There was a knock on the door.

“When I open the door—grab him!” Chick urged.

He waited. A hand tested the door knob. The door rattled a little.

“Open up!” came a muffled voice.

“Wait! Let him get anxious!”

A thumping came on the door.

Garry and Don grew tense. Chick’s hand was on the bolt.

It shot back.

“Now!”

Out they dashed, to encircle, to grapple with a figure standing off guard.

“Here! Stop that!”

The voice, deep and curt, made them draw back, look up at the form and face they released in amazed disappointment.

They had captured the Chief of Police!

“Uh—er—” Don stammered, “we—we expected—the—the ‘ghost!’”

“If you can prove you’ve caught him you can have my badge,” the good-natured officer chuckled. “As a matter of fact, I came in to see what was the result of your investigations. My men are all in the swamp, awaiting orders. We saw you bring in the Indians—they’re all out in the other room still, waiting for a report; your folks are, I mean.

“What have you got in the way of evidence, clues or proofs?” he asked.

They told him and showed him their bits of film.

“Wouldn’t stick in any court,” he stated. “Any finger prints are washed off long since, and the pictures could be cut from any news reel picture of airplane flights for observation purposes. No, boys——”

“We thought the ‘ghost’ would come to see what we had discovered,” Chick said lamely.

“Well, I’m not the ‘ghost.’ You’ll have to try some other scheme.”

“Don’t you think this ‘A’ and the figure ‘one’ might help?” asked Garry, indicating the smoked film, dimly showing the letters.

“It might—if there was anything to tie it up with.”

“If only we had the tracing of the Indian’s map,” Don said ruefully. “Or the blue-print Chick made—that had some sort of complicated figures on it—”

“Where is it—where is either one?”

“They were stolen, Chief.”

“Yes!—” Chick’s face became suddenly vivid with excitement, “yes!—but—when I made the blue-print, I picked up two pieces of paper and only discovered it after I had exposed the paper under the tracing!”

Hastily he switched off the white lamp, putting on the ruby light.

“I put the other sheet back, because it didn’t show much—but, you all know, there is a way to force up a stronger image—with intensifier chemicals.”

Feverishly Chick searched in the laboratory cupboard.

Garry aided him, while Don got the trays cleaned, and the Chief came in and closed the door.

Half an hour later Mr. McLeod caused the door to be opened to him.

“What’s going on?”

“Look!” Don’s trembling finger indicated a faint, but clearly discernible figure on a sheet of printing paper. The blue-print had been developed as far as it was possible to bring out the figure. Then a greatly under-exposed camera photograph had been made, on sensitive film, and this, by process of development known to Chick and the rest, intensified the lights and shadows which were more “contrasty” because of deliberate under-exposure. The result was a readable print.

There was the camouflaged map, apparently the hull outline of some old-fashioned ship, seagoing brig or privateer, with its sharply cut-under prow and overhanging stern, its roughly outlined deck and wavering waterline. Over that, distinguishable because in an ink that was dark and printed out whiter, was the outline of the airplane sketch.

“Camouflage!” Mr. McLeod agreed, “but——”

“Excuse me, Uncle!” Don interrupted. “If you will study that design, carefully, the way we have been doing for the past three minutes, and remember all that has happened, you’ll see that there are two clues in the camouflage. But we don’t want to stop to explain them. We want the ‘ghost’ to play his last ‘engagement’—and—we think he will!”

Then they walked out, in a group, to the larger room where the unsuspecting culprit waited.