And so it was agreed.

Ten miles south of Riga, surrounded by Russian airmen, they climbed into the craft which the Russian commander in the little city had provided for them. The plane was large and roomy, having a seating capacity of five.

Hal took his place at the steering wheel and Chester climbed aboard.

Still eyeing the flying craft suspiciously, Alexis followed Chester, and, sitting down suddenly, took hold of the seat with both hands and hung on for dear life, although the craft was still upon the ground.

Then he lowered his head and shut his eyes.

Hal gave the word, and willing hands started the machine along the ground. Gradually it gained momentum until it was skimming over the ground at a rapid gait. Then Hal threw over the elevating lever, and the machine shot into the air amid the cheers of the Russians below.

Alexis was conscious of a sinking sensation in the region of his stomach, and he ducked his head even lower as the car rose higher in the air.

"Look up, Alexis!" shouted Chester, reaching over and laying a hand on the Cossack's arm.

Now that the machine had reached a good height, Hal held it steady, and it darted ahead on a straightaway course. The plane shook with the vibrations of the engine, but otherwise there was scarcely a noticeable motion.

Now that the machine was more steady, Alexis, in response to Chester's command, slowly opened his eyes and looked about. Seeing nothing, he closed them again immediately, and again ducked his head. Once more Chester yelled at him to look about, and at last Alexis raised his head and glanced into the distance.

"This is a terrible place for a man to be," he muttered with a shudder.

"If man were meant to fly he would have been given wings. It is tempting the wrath of the elements to be here."

As he looked about him, however, and became conscious of the steadiness of the craft, his composure returned, and soon he was making inquiries regarding the construction of the craft, its speed and the height to which it could ascend. He glanced over the side of the machine, and then looked quickly upward again. The one glance below had made him ill.

He smiled faintly. "I can't look down yet," he said ruefully. "I suppose I'll get used to it in time; but now I had better keep my eyes inside."

"How fast are we going, Hal?" asked Chester.

"Sixty-five miles an hour," was Hal's reply.

Alexis was astonished.

"Sixty-five miles!" he e.j.a.c.u.l.a.t.ed. "Why, it seems as if we were standing still."

"If we were close enough to the earth you would soon notice the difference," said Chester.

For another hour they continued on their way without incident, and then Chester discovered the dim outline of a second aircraft trailing them at a distance. It was not gaining, but even when Hal put on more speed, at a word from Chester, he was unable to shake it off.

"Evidently a German," said Chester. "I suppose he wants to see where we are going."

For another hour the plane pursued them. Then Chester perceived that there were two instead of one, and that both were creeping up on them.

With a cry to Hal, Chester picked two rifles from the bottom of the car.

"We'll have to fight them off!" he cried.

Alexis stirred uneasily in his seat.

"I was afraid of it," he muttered. "Now, what will happen to me when I go hurtling through s.p.a.ce to the ground below?"

He shuddered.

Hal, in response to a command from Chester, slowed down suddenly. Taking careful aim at one of the pursuers, Chester emptied the magazine of his first rifle. There came from behind the sounds of screams, followed by an explosion.

"What was that?" cried Alexis in alarm.

"I got one of them!" replied Chester calmly. "The plane has gone to earth."

The second pursuing plane reduced its speed, but still clung on the trail of its would-be prey.

"We'll have to dispose of it some way, Hal," shouted Chester. "Turn quickly and run toward it, and I'll see if I can't send it to the ground."

He held his rifle ready as he spoke. Reducing the speed of the craft a trifle, Hal brought its head about in a wide circle; then darted suddenly toward the enemy.

But the latter was not caught unprepared, and a rifle bullet whistled close to Alexis' ear.

The giant Cossack clapped a hand to his head and for the first time looked toward the enemy. Then, reaching to the bottom of the machine, he raised up with a weapon, and, aiming at the hull of the enemy in the distance, poured the entire contents of the magazine into it. At the same moment a well-directed shot from Chester's rifle struck the pilot.

He sprang to his feet, spun around crazily, and plunged from the car. A moment later and the aeroplane blew up with a loud bang.

Alexis, who had seen the pilot go overboard, let out a cry of dismay. He could not help but think of the terrible fall to the ground.

"Good work, Alexis!" cried Chester. "I told you you would get used to it before long."

"I am not used to it," replied the giant, "but when a bullet whistles past my ear I get mad. I just naturally have to fight back."

Nevertheless he made a brave effort to appear unconcerned, and he took a look over the side. At that moment Hal allowed the car to glide slowly nearer the earth. For a moment Alexis was unaware of this sinking sensation; but suddenly treetops came into view, and the Cossack let out a cry of alarm:

"We're sinking!" he exclaimed.

Hal laughed.

"Just coming down to get a look about," he replied. "Now, if you will look over at the earth a few moments, you will soon overcome your uneasiness."

Alexis, taking a long breath, did so; and he continued to peer over the side, even after Hal, touching the elevating lever, sent the plane high in the air again.

Darkness fell and still the 'plane sped on. Then, so suddenly that they seemed to spring up from nowhere, the swiftly moving aeroplane was surrounded on all sides--as it seemed to the voyagers--by a score of hostile aircraft, while shots rang out from several sides.

Hal acted promptly, as had always been his wont. He allowed the 'plane to drop a good quarter of a mile with a sudden lurch, and then righting it, darted forward again. For a moment they had shaken off the foe, but the latter was not long in finding them. Searchlights flashed in the sky, seeking out the prey.

By a series of clever maneuvers, Hal succeeded in evading the hostile craft during the long hours of the night, turning first this way and then that, rising and falling. But with the first gray of dawn, it became plain to both boys that escape was practically impossible.

Looking down Hal saw water below him, and at the same moment the hostile air fleet ten 'planes strong, swooped down on them.

Chester's rifle cracked, as did that of Alexis. Bullets flew about all three occupants of the machine, and then the craft, struck in a vital spot, staggered. The 'plane began to sink slowly. In vain did Hal try to check the descent. The machine, still heading slightly toward the north, glided toward the water below.

Suddenly Hal made out something below besides water. It was land. The lad breathed easier, for it was plain, that at the rate at which the craft was sinking, it could clear the water by a good quarter of a mile, beyond which the lad could see a sandy coast.

"It must be the coast of Sweden or Denmark," he said to himself, "in which event we are safe, for it is neutral ground."

The Germans, realizing that their foe was sinking, did not waste another shot on it, but swarmed after. Now the craft was close to the water.

Gently it skimmed over it, across a short stretch of sand, and then settled slowly to the ground.