"Great Scott!" he exclaimed, and sank back again. "Out of the frying pan into the fire. Say!" and his voice rose a trifle, "What do we want to go to Belgrade for? What's the use of sticking our heads into a hornet's nest?"

"Look here, Mr. Stubbs," said Hal, again turning in his seat. "Don't you want to go to Belgrade with us? If you don't, I'll go down and let you off here."

He reduced the speed of the craft a trifle.

"No, no. Never mind," said Stubbs hurriedly. "I was just joking. Of course I want to go to Belgrade. They tell me that the Germans are just about to come in. But that won't make any difference, will it? No, indeed. Not to us. I suppose we are going to be there to welcome them.

I'll bet they'll be glad to see us."

The others smiled, but they made no reply to this outburst. They had known Stubbs long enough now not to pay much attention to him at times.

And this was one of those times.

Stubbs now turned a bit in his seat and spoke to another figure who was close to him.

"How do you like this kind of travel, Ivan?" he asked.

"I belong on the ground," was the brief response.

Ivan's face was a chalky white, but he was sitting tight and saying nothing except when it was absolutely necessary. Just behind him sat Nikol, and the latter seemed to be in a condition similar to Ivan. Nor did he make a sound.

Suddenly, as the aeroplane moved swiftly along, there came a loud explosion. The machine rocked crazily and Hal's prompt action at the wheel was all that saved the occupants from being pitched head-first into s.p.a.ce. He righted the craft with an effort.

"What's the matter?" demanded Chester in no little alarm.

"It's all over now," mumbled Stubbs with a groan. "Pray, Ivan."

The big Cossack seemed to have no doubt that it was all over and while he clung to the side of the machine with both hands, he mumbled strange words in his native tongue. Apparently he was following Stubbs'

injunction.

"I don't know," replied Hal, answering Chester's question. "Something seems to have gone wrong with the engine. Guess we had better go down."

He tilted the elevating levers and the plane descended gradually and swiftly.

Under Hal's firm hand it settled gently upon the ground and all immediately climbed out. Stubbs drew a great breath of relief.

"I never expected to reach here alive," he declared.

Ivan and Nikol also were plainly relieved. They said nothing, but the expression upon both their faces spoke plainer than words.

Hal bent over the engine. As he straightened up, Chester asked:

"Anything serious?"

"Believe I can fix it within an hour," replied Hal. "I'll have a try at it, anyhow."

"Need any a.s.sistance?" asked Colonel Anderson.

Hal shook his head.

"Nothing you can do, I guess," he replied.

"Then I am going to take a little prowl into these woods here," said the colonel, indicating a small clump of trees that stood perhaps a quarter of a mile to the east.

"I'll go along," said Chester. "I feel like stretching my legs a bit."

The two walked away together. Ivan and Nikol remained behind and watched Hal tinker with the engine.

Chester and the colonel prowled about among the trees for the better part of half an hour and then turned to make their way back to the machine. As they walked along, Chester suddenly caught Colonel Anderson by the arm, stopping him in his stride.

"Sh-h-h," muttered the lad and listened intently.

"What's the matter?" demanded Colonel Anderson, in a low voice.

"Thought I heard voices," replied Chester. "Listen."

Both became silent; and directly they caught the sound of a low voice off to the right. Then there came a second and a third voice.

"Don't see what they can be doing here, whoever they are," declared Chester in a whisper. "We'll see if we can get a look at them."

He led the way softly in the direction from which the voices had come.

The voices became louder; and directly, parting two large bushes, Chester made out the forms of three figures not ten yards away.

He turned quickly to Colonel Anderson and laid a finger to his lips. The colonel approached cautiously.

From the spot where the two stood it was possible to see the three men in front of them without danger of being seen themselves, for they were screened from sight by the large bushes. One of the men was attired in what Chester took to be a Serbian uniform, but the others were in civilian attire.

"We'll do a little eavesdropping," whispered Chester.

Colonel Anderson nodded and they became silent.

"So you say that everything is ready for Bulgaria's entrance into the war?" spoke the man with the uniform.

"Yes," replied one of the others, a man of perhaps forty years of age, with a long flowing beard.

"And she will strike when?"

"The moment Belgrade has fallen before the Germans," replied the third man, who, the watchers saw now, was little more than a boy, smooth of face and bright of eye.

"And they will strike where?"

"At the Anglo-French force being rushed from Saloniki to the aid of the Serbians."

"Why wasn't I kept posted on all this? How was I expected to do my part here, being left in ignorance of diplomatic affairs?"

"I don't know anything about that. All I know is that we were ordered here to learn what success you have had in undermining the Serbian officials. Also to get your views upon which way the Serbians will retreat."

"Well, I can tell you that in a few words. I have had very little success with the Serbians. They are loyal to their cause and seem determined to fight to the last ditch. But I did get close enough to one man--a member of the general staff--to learn that in the event of reverses to Serbian arms, the Serbian army will retreat into Greece."

"So? I had deemed it most likely they would fall back and join the Montenegrins."