"You probably will see it soon enough," returned Chester quietly. "Even now you can hear the booming of the great guns without. The Austro-Germans are moving on Belgrade and it will only be hours before the Serbian retreat begins."

The conversation continued along various lines until the return of the Serbian commander, General Save.

"If you will come with me," he said to Colonel Anderson, "I will see if you can identify the traitor. Which of your friends here was with you?"

Colonel Anderson nodded toward Chester.

"Then he shall come, too. The others may remain here until we return."

Hal, Ivan and Nikol were undeniably disappointed at this turn of affairs.

Not so Stubbs.

"This comes nearer being what I call comfort than anything I have enjoyed since coming across to Europe," he said, settling himself in the commander's easy chair and drawing exhilarating puffs from his pipe. "I don't care how long we stay here."

"Mr. Stubbs," said Hal, "I am afraid you are lazy."

"Mr. Paine," said Stubbs, "I know I'm lazy."

Leaving the general's quarters, Colonel Anderson and Chester accompanied the Serbian commander toward the front.

"The enemy has begun his advance," General Save explained, as they walked along. "He is attacking in force all along the line. We are resisting as well as we may. That is why every available man has been sent forward. We will find the traitor there some place."

"And do you have any hope of holding back the enemy, sir?" Chester asked.

"None," returned the general quietly. "We will resist to the last, but even now preparations are being made for evacuating the capital. With the coming of darkness, the retreat will begin. We shall fall back to Nish, which, I trust, we shall be able to hold until Anglo-French a.s.sistance arrives."

"I hope so, sir," declared Chester.

"And as soon as you have picked out this traitor for me," said General Save, "I will ask you to undertake a mission for me."

"We shall be glad to be of service, sir," replied Colonel Anderson. "And the nature of the mission?"

"Why," said the commander. "I have information to the effect that the Anglo-French troops are already on the way from Saloniki. They may not know of the real seriousness of our position. Communication has been hampered for the last few days. I will send word to them by you."

"Very well, sir," said Colonel Anderson. "We shall be glad to go."

"Now keep your eyes open," said General Save, as they came for the first time among the Serbian troops, the men farthest from the front, men being held in reserve.

Among the regiments the three pa.s.sed slowly, scanning the face of every officer; and they came upon their man sooner than they could reasonably have hoped.

Chester suddenly touched General Save on the arm.

"Look! There he is!" the lad said in a low voice.

The general glanced in the direction indicated. Perhaps twenty yards to the left, engaged in conversation with an officer who wore colonel's stripes, and a man whom General Save immediately recognized as one of the general staff, stood the person the lads had seen in the woods a few hours earlier. "Are you sure that is he?" demanded the Serbian commander.

Chester nodded his head vigorously.

"Certain, sir," Colonel Anderson agreed.

"Very good. Then come with me."

The general approached the group of officers, who stood respectfully at attention when they perceived his approach.

"Captain Dellse!" said the General.

"Sir," replied the officer, stepping toward the Serbian commander.

The older officer looked squarely into the man's eyes for several moments without saying a word. The traitor tried his best to return the general's steady gaze and for a moment he succeeded. Then his eyes wavered slightly.

General Save extended his right hand.

"Your sword, sir!" he commanded.

The other staggered back and his face turned a ghastly white.

"Wha--what, sir?" he stammered.

"Your sword," repeated the general calmly, his hand still extended.

With a visible effort the other pulled himself together.

"I do not understand you, sir," he said, with a subdued air of insolence, glancing quickly about at the others who now surrounded him.

General Save lost all patience now. He took a step forward.

"Give me your sword, you traitor!" he commanded angrily. "You are under arrest. You shall be shot in ten minutes."

The face of the accused officer turned livid. There was no pretending to misunderstand now.

Quickly he glanced about him. Chester and Colonel Anderson, in their civilian clothes, stood each with a hand in his right coat pocket, and in the hand of each rested a little automatic.

An ever increasing group of Serbian officers also surrounded him. The man with whom the traitor had been engaged in conversation moved gradually toward the rear of the circle. General Save caught sight of him out of the corner of his eye.

"Colonel Breyold!" he commanded.

The other halted.

"Come here, sir," commanded the general.

Glancing furtively about him, the other obeyed. The Serbian commander turned to another of his officers.

"Relieve Colonel Breyold of his sword," he commanded.

Without waiting to see that his command was carried out, he stepped close to Dellse. The other gave way before him and with a sudden movement produced a revolver.

Before those nearby could interfere, he had raised the weapon and pulled the trigger. There was a sharp report, a flash of fire, and when the smoke had cleared away, Dellse and General Save were locked in each other's embrace, struggling furiously.

With loud cries other Serbian officers jumped forward and separated the combatants. Dellse's weapon was wrested from his grasp and in a moment he was powerless.