“We can’t out-run him, Hal,” shouted Chester.

“Then we shall have to try something else,” was the reply.

Abruptly he reduced the speed of the craft and the Austrians dashed in range of the revolvers of the fugitives almost before they could have realized it.

“Crack!  Crack!”

Chester and Colonel Anderson had fired.  There came a scream of pain from behind and the Austrian craft wobbled crazily.  A moment later a man sprang to his feet, sought to retain his footing, threw up his arms and went hurtling into space.

“Got one, Hal!” said Chester, quietly.

“Good!”

Came a volley of small arm fire from behind and bullets whined about the four friends.  Again Chester and Colonel Anderson fired almost simultaneously and again their efforts were rewarded.  A second man was put out of the fight, as they could see.

At this moment Stubbs came into action.

He arose from his seat and, grasping the side of the speeding craft with his left hand for support, stood to his full height.  His right arm drew back, then flashed sharply forward again and a small object went spinning through the air toward the Austrian airship.

It struck home and there was a terrible explosion, followed by several sharp cries of pain, as the Austrian airship seemed to split into a thousand pieces.  A moment later these pieces disappeared.

The three friends turned upon Stubbs.

“What is this, magic?” asked Chester in surprise.

“No,” replied Stubbs, quietly.  “Melenite.  I just happened to see a stick of it here, so I threw it.”

“Well, you did a pretty good job, Stubbs,” said Colonel Anderson.

“I didn’t pitch for my college team two years for nothing,” returned Stubbs modestly.  “But now let’s go down.  I want to get my feet on the ground again.”

“It won’t be much longer, Stubbs,” said Hal.  “Another two hours at this speed should put us across the Serbian frontier.  Just be patient.”

“I’ll wait,” replied Stubbs, “but I won’t promise to be patient.”

He sank back to his place and refused to talk further.

While the big army craft is speeding across Austria it will be a good time to explain the presence of the four friends in their present predicament and introduce them briefly to those who have not met them before.

Hal Paine and Chester Crawford were both American lads.  With the former’s mother, they had been in Berlin at the outbreak of the great war, and, after a series of interesting and exciting adventures, they made their way to Liege just in time to take part in the defense of that stronghold with the Belgian army.

There they won distinction and lieutenancies in the Belgian service, the latter bestowed upon them by King Albert himself.  They had been in France with the British troops that had stopped the German drive on Paris and had gone with the Allied army on its advance.  They had seen service on all fronts and now considered themselves veteran campaigners.