Feverishly Don worked with spare cable to wire around the ignition switch and get his engine going.

From the boathouse staggered Garry and Chick, coughing, their eyes streaming. They dragged, by the shoulders, the unconscious pilot.

“His head must have struck something!” gasped Garry, dabbing at his eyes. Suddenly something snapped into his mind.

“Chick!” he choked and gasped, then turning, stuttered, “my first aid—kit! I left it—on—path—promontory—when—mail ’plane went down!”

Staggering, but bravely eager to help a man who was hurt, the youth took his way off the wharf, along the path, into the grass toward the end of the shore that curved out into the inlet, making the wavering line of the channel on one side.

The roar of an airplane engine came—but it was in the air!

Don looked up. There was the Dart, coming over, shooting the water landing, making its approach, coming in, setting down!

He recognized, at its controls, as he flung aside his helmet, the pilot who had been injured in the first crack-up, the night they saw the apparition: he had been driven down from the farm by its owner and was sufficiently healed in his arm to handle stick and throttle.

With him was the Police Chief.

“Get him?” hailed the officer, as the gas was cut and switch put off, and as Don shook his head, shouting his explanation, the Dart ran up close to the wharf.

“The swamp is surrounded,” the Chief cried. “We let them all go, as you had planned. Didn’t the culprit walk into the trap?” Don told him breathlessly what had happened, urged that the Dart go aloft and scout.

The Chief urged Don to occupy his place, while he attended to the man over whom Chick was working incompetently.

Don hesitated: they might need to use the Dragonfly, also, he protested. The newly recovered pilot suggested that Don fly the Dart, reconnoitering, as it was the less stable ship and in his condition he preferred the steadier, more easily controlled craft. They began the exchange, listening for a motor. No sound came.

Garry, recovering his strength, if still teary-eyed, blundering along to find his abandoned first aid kit, saw the Dart go in, and felt that for all his bravado, Mister Spook was almost as good as captured.

He broke through the tall grasses, near where the path ended.

His eyes saw an amazing sight! There, where the mail ’plane had gone into the mud, fresh planking had been laid across the mud, and on it rested the airplane, the boards concealed by wings and a camouflage of cut grass: its broken hull had been re-covered, freshly doped. It had no pontoons; but on each side of the fuselage slanted auxiliary wings of thin boards had been attached by wire. If it could be started and raced off the board support, he saw, the slanted planks would serve to lift it higher with each gain of speed, as a boat of the speed type is lifted by its side-flanges. And—in his disguising garments, Scott was working feverishly at the motor. Garry leaped forward. Scott tore off his mask to show a face of fury and dismay.

“Stand back!” Scott lifted a small missile. Garry knew the tear-gas and its effect. He hesitated.

“Shame!” he cried. “You can’t escape. Even if you did fool us by taking us to look for your own self, at the start, you can’t fool us any longer.” He was talking against time, getting his feet set.

“Come and turn that prop, or I’ll—throw this!”

Garry changed his tactics; meaning to leap, ducking the missile, he altered his plan. “All right!” he agreed, docile with pretended fear.

He moved toward the propeller, stepping on the edges of the boards.

He saw the electric crash launch floating just beyond the nose of the ship. Menaced with the tear-gas, he nevertheless made his leap, across the water, from the planks, that gave under him, to catch the coaming of the boat’s cockpit. The missile flew through the air after him, but Garry, in the channel, went down, until his feet touched mud; holding his breath he swam under the launch, coming up on the other side. He trod water, concealed.

To his dismay he heard the man, discarding his disguise, twist angrily at the propeller of the repaired airplane. It caught on a firing point of the engine, swung rapidly. The man rushed along the planks.

Drowned by the noise close at hand, Garry failed to hear the Dart rev up its engine, turning to get into the wind.

In it was Chick and at its controls was Don. Garry disregarded all danger, clambered into the boat, tumbling in close to the wheel and switch. He tore at the latter, sending current into the motor. With a howl of rage Scott drove his airplane off the makeshift runway and straight at the launch. He hurled a missile. It did not strike the boat.

Garry backed water, up the channel. The airplane had to take the air or foul its wings in grass. It rose. A bomb dropped—Garry, full speed astern, avoided it and backed up the channel. He could not turn.

Up soared the Dart. It came around. Don saw the mail ship turning to cross the bay. Full-gun, he took up pursuit, heedless of the Chief’s warning that their tear-gas, brought in case the swamp yielded the culprit, had been taken, must be in the hands of the escaping Scott.

Seeing that the Dragonfly’s pilot had trouble with his arm, Don knew he alone stood between Scott and escape.

The Dart was fast. So was the mail ship, once free of the water.

Garry, backing up the channel, saw Don fly over. He kept on, until he reached the wider sheet of water, backed around, swung close to the Dragonfly, climbed aboard, and feverishly begged to have a chance at the controls. The other pilot, not too strong, yielded. The Dragonfly started.

Don climbed, losing some advantage; but he knew that it would be a long chase—wanted it to be so. The man in the mail ship, with his bravado serving to the end, lifted and showed strings of jewels that flashed vividly in the first rays of the rising sun.

Don saw that Scott meant to cross to Connecticut. It would be a run across Long Island Sound. Don did not want to drive down the ship over water—he would lose the treasure.

He saw, far behind, the Dragonfly.

The crossing was made in record time, and then Don, in a ship easily maneuvered, raced up above the other. Then Chick screeched a warning.

Up toward them came one of those missiles—a tear-gas bomb.

Don made a quick barrel-roll. It caused the bomb to miss him.

Falling, the missile was in the path of the mail ship. Straight into it, as it fell, Scott raced. It smashed in his cockpit.

Doomed by his own act, he lost control, and in a slanting, catapulting dive, struck just beyond the shore line, on firm earth.

And thus the Ghost of Mystery Airport passed.