Up to the dark room Don hurried with Garry.

At their knock a muffled voice came through the panels, hardly to be understood because of the weather-stripping used to make the joining of door and frame light-tight.

“He says he can’t let us in,” Don caught the faint murmur and interpreted it.

“Taking the film from the tank, I guess,” Garry responded. “We’ll have to wait.”

Five minutes passed. Then the door was opened.

Chick, with hands stained by contact with pyro and other chemicals, showed a disappointed face.

“No go!” he greeted his chums. “The hangar light fogged the film. It was light-struck, all right.”

“How about another test, from the inner end of the roll?” Garry suggested.

“We can try that,” agreed Chick.

Into the intense blackness of the room they crowded, and, by sense of touch Don extracted from the inner spool of the roll, an inch or so of film, while Garry washed out the developing tank used for the films they took of new craft for making half-tone engravings, pictures for circulars, catalogues and “trade paper” illustrations.

Chick, mixing a fresh charge of pyro, with sodium sulphite and the right amount of carbonate, from ready-prepared packets, enclosed the film in a roll of rubber-edged material that let the developer seep in but keep the fabric from touching the delicate film surface.

“Get the tank lid tight,” he warned Garry after the solution had been mixed and poured in, the film container being swished up and down to get the film full impregnated. “I have to light the bulb to time it and get the temperature of the mixture by the thermometer you just had in the tank.”

“Go ahead—it’s tight.”

They allowed twenty minutes for development; then the light was extinguished and the door, opened for ventilation, was closed.

In darkness Chick removed the film, handling its container gingerly as he immersed it in the hypo fixing bath to “set” the image. They gave it about half a minute of darkness in the fixing bath.

“Now we can see it,” he decided. “Switch on the——”

The door swung sharply outward.

There came a blinding flash, and with it the dense smoke of some pungent, gas-reeking chemical. Eyes smarted and watered. Staggering back from the surprise attack, totally unexpected, Don, Garry and Chick took an instant to cower back against the wall, shielding their faces.

There was the play of a flashlamp about the room.

Then, before either of them could recover from astonishment and from the choking smudge enough to move, there came the clank of some metal, and the slam of the door.

“Oh!” Chick gasped, and then said no more, choking in the smoke of the bomb or whatever poured its dense, stifling smoke up, filling the small, almost airtight compartment.

It took Garry, nearest the door, half a minute of choked, almost suffocated effort, fumbling in the dark, to get the handle of the door and twist it. The door was not locked; but, as he dragged Chick out and Don leaped over the fuming, pungent smoke-flare that had been ignited and dropped in the dark room, Garry saw that the rubber catch-all mat on the floor was burning.

The designing room, with its unreplaceable, valuable files, was adjacent to the dark room. Below, in the workshops, “dope” and other dreadfully inflammable materials lay stored. In the hangar next it were airplanes worth thousands of dollars, including a fourteen-ton, double-bodied seaplane that had been ordered by the Mexican Government.

“One go one way, the other to the bank stairway—or the fire escape!” he screamed to Don and Chick.

Himself, ignoring the lost film—knowing well that was what had vanished in the hands of their adversary—Garry raced for a fire extinguisher.

Choked, blinded, staggering, Don and Chick heard, but had difficulty getting their bearings.

Garry ran, full speed, back, to upset the chemical fire extinguisher so that its contents, mixing, would generate a gas to drown out the small, but menacing fire that had already touched the matting running from the designing room corridor across that side of the space.

Don staggered to the window, drawing in great lungfuls of fresh air.

Gasping, choked, he strained his eyes toward the grounds outside. Chick, at the corridor door, looked up and down, bracing against the dizziness that swung him on his unsteady legs.

Garry drenched the matting, the smoking flare, the floor and walls in danger.

The fire out, he dropped the extinguisher, and turning, raced, with Don and Chick, recovering rapidly, at his heels. He, too, was choked; but at the first opening of the door Garry had, fortunately, thrown a sleeve protectingly across his face, so that he had breathed less of the fumes than his companions.

Up to the control tower balcony raced Garry. Don went down to the hangars. Chick took the midway corridor, searching each office.

“There he goes,” shouted a voice.

Garry, rushing to the balcony, saw a fleet figure running across the grounds, out of the good light, but discernible. Into the searchlight Garry ran, while Don and Chick, hearing his shouts of response to the voice from below, went, careless of risk to limb, down the stairways at front and back of the big building. Garry, struggling to get the searchlight turned in the proper direction to pick out the fleeing figure, to identify it in a flare of vivid light, explained swiftly to the control chief on duty.

By the time the light was in position, on the roof, and its mechanism adjusted, the beam probing the velvety dark night picked up a scene of swift action.

Don and Chick, close to the hangars, were running, full tilt, out of the grounds, along the roadway.

A hundred feet beyond them were two heavier figures, pounding along at a slower pace, so that Don and Chick soon met, passed and out-stripped them.

Just beside the cottages that were boarding places and providers of furnished rooms for airport mechanicians, shop workers, pilots and others, a fleetly running, light form swerved out of the light just as Garry got to the balcony again.

Behind a house the figure vanished.

It had some round object clutched in the crook of an arm, Garry thought.

Standing there he watched until Don and Chick reached the spot.

In the bright rays of the light they soon returned, waving arms in dismay. While they stood, undecided, a window of the nearer cottage flew up.

Garry could not hear the voice, but he recognized Scott.

He watched as Don and Chick, calling upward, waited, received an answer, turned and raced back toward the hangars.

The upswung arm of Don, the upward pointing finger of Chick, told Garry what was wanted.

Down the stairways he plunged.

“Quick! Henry—help me!” he shouted, running toward the Dragonfly.

Don appeared at the door.

“That’s right!” He saw Don pushing at the tail of the aircraft.

“What’s it all about?” demanded the mechanician, to whom all this in-and-out pushing of the “busses” was mystifying.

“Scott called down to us. He was dozing when the light woke him. He got a glimpse of the man running away,” Don informed him.

“It was the Indian—John Ti!” contributed Chick, putting his weight behind the wing of the ship as he helped get it through the doors.

“Well—then he went into the swamps!” the man said. “That’s the only place he could get to from back of that house.”

“I know it!” puffed Garry.

“What do you want this crate for, then? You don’t expect to see a single, Indian kid, hiding in a pitch-dark swamp!”

“No!” gasped Don, “we don’t. But—Henry—we left the Dart tied there!”

“Get all the flares you can find!” Garry urged Chick, himself busy looking over the fuel gauges and oil supply.

Chick raced away, fully recovered.

They got the Dragonfly into the air in short order.

Three determined youths, each tightly strapped in place, each with a supply of signal flares, of rockets, of flash bombs, of white, red, blue and green Verey lights, went forth into the sky lanes, determined that their clue, considered important by Scott, should be recovered.

In the swamp a lithe figure, watching, seeing the ship coming over, muttered.

“He shan’t get away!” Don whispered, half aloud, to himself, in the Dragonfly.

“He shan’t get away!” muttered the lithe figure swiftly untying the Dart beside the boathouse wharf.

To which an older, more deeply copper-colored form grunted agreement, whirling the fight propeller to “contact!”

Then began a most peculiar sky chase!