“You want to be careful crossing the Balkans.  I understand there are some British and French aircraft with the Serbians and Montenegrins.  Look out for them.”

“I’ll be on guard,” replied Hal.  “Thanks for the information.”

“Tell you what,” said the Austrian, “I’ve been doing some scout duty there myself.  I’ll just trail along.  May be able to help you out a bit”

Hal didn’t think much of this plan.

“I can make it all right myself,” he declared.

“Suppose you can,” was the reply, “but it is just as well to be on the safe side.”

“Well, suit yourself,” said Hal, “but don’t expect me to wait for you.”

“If you can distance me you will have to travel,” returned the Austrian.  “I’ve the fastest craft in the service.”

“I’m glad to hear that,” replied Hal, and added to himself:  “I don’t think.”

“Set your pace,” continued the Austrian.  “I’ll trail along behind.”

“No use talking any more, I guess,” Hal muttered to his friends.  “May as well go along.”

Chester and Colonel Anderson nodded their assent and the machine moved forward again.

Things might have gone well had it not been for Stubbs.  Suddenly the little man uttered a yell and sat up straight in his seat.

“Ouch!” he shouted.  “I’ve got an awful pain!”

CHAPTER II.

Montenegrin mountaineers.

Hal drew a sharp breath and tightened his hold upon the steering wheel.

There was no question that Stubbs’ voice had carried to the occupants of the second craft, and as Stubbs had exclaimed aloud in English there was little doubt in the minds of our three friends that the Austrians would seek an explanation.  Nor were they wrong.

Came a hail from the Austrian: 

“Who’ve you got aboard, there?”

“Prisoner,” replied Hal, thinking quickly.

“What are you doing with him?”

“We—­” Hal began, but the Austrian interrupted.

“Spies, that’s what you are!  Down to the ground now, or I’ll put a hole through you.”

“Guess it’s no use fooling any longer,” muttered Hal.

He threw over the elevating lever and the large craft soared rapidly.  At the same moment a shot rang out from aboard the Austrian, followed by a cry of surprise, and then the Austrian gave chase.

“Get your guns and see if you can pick ’em off,” Hal instructed Chester and Colonel Anderson.  “I’ll run this thing, but you fellows will have to do the fighting.”

“Suits me,” responded Chester, examining his revolver carefully.

Colonel Anderson also nodded his agreement to this plan.

Hal now changed his course and the airship headed toward the south, bearing off a trifle to the east, in a direction that he believed, eventually, would land them in Serbia.

It became apparent now that the Austrian had not boasted of the speed of his craft without reason, for he gained perceptibly.