Suddenly, through all the turmoil of shattering explosions, tossing air-currents and drifting, acrid smoke, he became conscious of a sudden, swift-flying pursuer.

By the light of the burning Plant, down there somewhere in the vapors of the thunderous Falls, he saw a hawk-like ’plane that swooped toward him with incredible velocity, savage and lean and black.

Off to the right, a sudden spattering of shots in mid-air told him the battle in the sky was likewise being engaged.  He saw vague, veiled explosions, there, then a swift, falling trail of flame.  A pang shot through his heart.  Had one of his companions fallen and been dashed to death?  He could not tell—­he had no time to wonder, even, for already the attacker was upon him, the swift Air Trust epervier, one of the dreaded air-fleet of the world-monopoly!

Gabriel had just time to swerve from the attack, and swoop aloft—­dropping his next to last projectile as he did so—­when the whirling shape zoomed past, swung round and once more charged.  He saw, vaguely, two men sat in it.  One was the pilot, a “Gray” or Cosmos mercenary.  The other—­could it be?  Yes, there was no mistaking!  The other was Slade himself, commander of the hireling army of Plutocracy!

Out from the attacking ’plane jetted sadden spurts of fire.  Gabriel heard the zip-zip-zip of bullets; heard a ripping tear, as one of his canvas wings was punctured—­God help him, had that explosive bullet struck a wire or a stay!

Then, maddened to despair; and burning with fierce rage against this monster of the upper air that now was hurling death at him, he once more “banked,” brought his machine sharp round, and charged, full drive, at the attacker!

This tactic for a second must have disconcerted the Air Trust mercenaries.  Gabriel’s speed was terrific.  With stupefying suddenness, the epervier loomed up ahead of him.

“Now!” he shouted.  “Take this, from me!”

Half rising from his seat, he hurled his last remaining projectile full at Slade, then wrenched his own ’plane off sharply to the left.

A thunderous concussion and a dazzling burst of light told him his chance shot had been effective.

He got a second’s vision of a shattered black mass, a tangle of girders, wires, collapsed planes, that seemed to hang a moment in midair—­of whirling bodies—­of wreckage indescribable.  Then the broken debris plunged with awful speed and vanished through the red-glowing mist.

Even as he shuddered, sickened at the terrible, though necessary deed, the deed which alone could save him from swift death, an overwhelming air-wave from the terrible explosion struck his speeding machine, the machine captured in the Great Smokies from the Air Trust itself.

It heeled over like an unballasted yacht under the lash of a hurricane.  Vainly Gabriel jerked at wheel and levers; he could not right it.

As it seemed to come under control, a stay snapped.  The ’plane swooped, yawned forward and stuck its nose into an air-hole, caused by the vast, uprising smoke and heat of the huge conflagration beneath.