Clearly Don saw, as his helicopter wavered, teetering like a dizzy baby trying to stand alone, the venomous purpose behind that air disturbing swoop.

Chick, staring with wide eyes, his heart stopped, felt the sway and quiver of the cockpit and convulsively snapped the clasp of the safety belt he had released to operate the projector.

Up, in a zoom, after his furious dive, the mail craft’s pilot sent his ship. On wingtip, he came around.

Garry saw his intention.

So, too, did Chick and Don.

The dive had sent the angry flyer down a steep dive, past the helicopter and up, again, in a climbing zoom, to a high point on which he turned to come again past the other aircraft.

Garry realized that the man in that ship of doom was beside himself with passion, beyond reason. Don’s hand pressed the throttle. His own engine revved up smartly. The upper blades whirled faster.

“Can he climb away in time?” Garry gasped. Mr. McLeod, behind him, shouting, futile, helpless, gave up waving his arms at the mail flyer and watched Garry with wondering eyes as the young and inexpert pilot at the controls of the Dragonfly began also to increase his speed.

Don, opening up his fuel feed, felt the top fan catch in steady air, saw the needle of his altimeter tremble, begin to move forward. His tractor, or pulling propeller, also operating, began to show an effect.

But whether he climbed, at the same time moving forward, or not, the mail flyer could so adjust his next dive that it would sweep the helicopter’s air with that deadly, upsetting propeller wash. Garry, too, realizing that, came, as best he knew how, to the rescue.

With his flying speed picking up rapidly, he drove straight across the area between himself and the mail flyer. His eyes, watchful and narrowed, caught the instant at which the flyer ahead dropped his nose.

His own ship dropped its nose, and, with throttle, open wide, giving his engine full impulse the intrepid youth darted straight for the area where he judged that the other man’s dive would bring him.

Carefully, so as not to spoil Don’s own air too much and thus do what the mail flyer sought to accomplish, yet making his attack as close as his inexperience told him was safe, Garry drove for the point where the other diving ship should come.

That dive of Garry’s spelled an instant’s respite for Don. With a right foot slightly pressing rudder bar, Garry swung the Dragonfly in a gentle arc, as he went down, so that his path of flight went as far to Don’s side as possible: at the same time he would come back, he felt, into a line that must either bring the mail ’plane and his ship close, or the other, disturbed and disgruntled by his unexpected tactics, must side-slip out of danger.

That was not quite the result.

The mail ship, its control man seeing Garry’s purpose, drew up his nose, kicking rudder and banking—he sent the ship into an upward, sidewise skid.

It accomplished Garry’s purpose. Don, climbing and moving forward at the helicopter’s best speed, was out of the danger zone.

The few seconds of advantage he gained meant safety, because he had the helicopter righted and working under perfect control again.

Garry, cutting the gun, not skilful enough to dare sharp maneuvers, went on for some hundreds of yards before he thought it safe to bank and turn. A swift glance sidewise and backward showed him that the mail ship had come out of its skid, righted and again was executing a wingtip turn.

“Won’t the idiot ever give up?” Garry muttered.

Chick, watching the scene, unable to take part, saw one point of possible advantage, if he could only communicate with Garry.

In its climbing, forward position, the helicopter was close to the same altitude that the mail ship then had. Garry, in his last maneuver, had lost a considerable amount of altitude, and was, thereby, too low for anything but a climb.

Still, as Chick almost instantaneously thought it out, if Garry drove forward on a straight line, the imminent dive of the mail pilot would bring him into danger of a crash with the Dragonfly—if only Chick could get Garry to fly forward, on a level, at once, to get to that essential point where he would be in the required position, the mail pilot must turn.

With wildly waving arms Chick tried to attract Garry’s attention.

The young amateur, busy watching his controls, the steadying of his ship, planning his next course, did not at once see Chick’s movement.

Chick reaching forward, caught the detonating mechanism of the Verey pistol, which he knew Don had told him to load after their last signal.

Chick fired the green Verey light.

That made Garry turn his head.

With the pilots’ code, arm movements, Chick beckoned to Garry, as he saw the youth turn his head that way: quickly, then, Chick held an arm straight out in front of him. Rapidly he repeated the gestures.

As he began again to beckon, Garry, catching his idea, revved up, his ship came on, level-keeled and swift, just as the mail ship began to come forward, itself on a power-glide of an angle to bring it close to the helicopter.

But Garry, coming fast, saw the value of Chick’s signal.

Full-gun, he used every ounce of power, every hope of his earnest young championship for Don and Chick, to send that craft of his into place in time.

The mail ship’s control man saw that if he continued to come at the helicopter he must come also into a line of flight that would intersect that of the Dragonfly.

Unafraid, determined, if need be, to risk all to save Don from the vicious doom intended by the infuriated, senseless man who had tried to avenge a mistaken idea of the helicopter’s purpose, Garry held on.

The mail ship swerved away long before it came near Garry and the Dragonfly. Don, its pilot saw, would be above any safe dive he could make, and he suddenly changed his tactics, swerved and then, kicking rudder and banking—but in the wrong direction with respect to making a turn—the mail ship following its controls, skidded upward, straight for the helicopter.

But its pilot did not want a crash.

He thus got into a position where his sudden restoration of balance put him just forward of the helicopter.

There, revving up to full speed, he sent back over the tail of his ship that most terrible of all man-made winds—the straight, hard fury of his propeller blast.

Don felt the helicopter stagger.

With all his hope gone he felt sickish, as the blast came. Not alone his own, but Chick’s life, too, was about to be the payment for an impulsive plan.

But that Power above and beyond man’s puny hates, sometimes called Luck, oftener known as a good “break,” had caused the mail pilot to neglect to return his elevators to neutral; slightly raised, the tail surface caught the full effect of his own deadly slip-stream, sending the nose sharply upward, and thus making that fury of disturbed air pass only the tractor propeller of Don’s craft—so that its upper blades at their best speed were able to draw him up beyond the danger of worse than an instant of horrifying danger.

Stalled, the mail ’plane fell away, and its pilot had his work cut out to avoid a bad stall. Over the bay, although the clouds concealed it, the mail ’plane, without pontoons, must quickly get flying speed, or plunge.

Don, still rising, and Garry, flying toward the swamp, saw another airplane, with the unmistakable markings of the Government service, come swooping from a higher altitude.

Two red Verey lights, the imperative order to land at once, flashed out from the newcomer’s signal firing apparatus.

That new craft meant business, was commanded by some one in authority.

Going, on his glide, below the cloud scud, Garry circled out over the bay, came around to face the light breeze, took the water with his pontoons and shot toward the landing stages.

As he skittered over the surface he saw crowds rushing about in the wide area covered by the landing lights; evidently everyone driving home from late picture shows and dances had heard the bellowing siren; the airport day force was on hand; feverishly they worked to get the first mail craft off the runways, as the second came in.

Two handlers caught the Dragonfly’s wing as Garry drifted it to the landing stage. Further out on the bay, Don set down the helicopter, to Chick’s intense relief, without a jar. Shutting off the top blades the young flyer used the tractor prop to draw him to the place vacated by Garry.

On the landing wharf Don, as he made sure that Chick was again in possession of his normal color, saw Garry, in the lowered rays of the spot and other lights, surrounded by a group.

Doc Morgan was there, he saw. So, he was surprised to see, were the two Indians, old Ti-O-Ga and his son, John.

Cars were parking everywhere they could find space. Excitement was in the air.

“We’ve got a lot of company waiting for us to come home,” Chick whispered, with an uneasy grin.

“I don’t like it much,” Don responded. “Especially not the man in that ship that ordered us down. He looks angry, from here.”

“Well!” Garry pushed past the crowd assembling around Don and Chick, “Don, do you hear what they’re saying in the crowd?”

“Yes,” admitted Don, looking around.

“We’re elected,” muttered Garry. “They say the Ghost of Mystery Airport is caught!”

Mr. McLeod, behind him, frowned.

“I wish you boys had shown some sense,” he told the trio. “It’s all very fine to discover methods, and to tell others how mysteries are worked; but it is pretty dangerous to show off when mail is being brought in. That man in the other ’bus is a postal inspector, by his looks—or an army man out of uniform.”

“I know we were hasty,” Don said ruefully, “but—we will have to face the music.”

“I don’t think we’ll like the tune very much,” Garry observed.

“No,” agreed Chick, “Garry’s pretty sure to lose his flying license, at the very least.”

The curt summons delivered by the man who came to them from the last land ’plane to set down, shoving his way through the crowd without ceremony, proved that there was basis for their uneasiness.

“Well, young man,” the newcomer snapped, “you and your scapegrace friends will come with me, unless there is some one here, in authority who will guarantee your safe arrival before the New York Chief of my department at nine in the morning. You can’t fool with mail, trying your tricks and stunts to delay the mails—especially air mail!”

While Mr. McLeod conferred, sponsoring Don and his chums, Chick put a hopeful look on the face he turned to his comrades.

“We’ll have the real ghost by morning!” he whispered.