The general bowed to them and took his departure, leaving them alone in his quarters.

From without a heavy cannonading could be heard.

“I guess the last advance has begun,” said Chester slowly.

“You probably are right,” agreed Hal.  “And I feel sorry for these Serbians.  If the British and French could only get here in time.”

“Well, I don’t see why they don’t,” declared Chester.  “England has promised more than once since the war began that she would not permit Serbia to be crushed.  Seems to me she should have taken some decisive action before now.”

“You forget,” said Colonel Anderson, “that England has her hands full in other parts of the great war theater—­France, Belgium, the Dardanelles, Egypt, India and Africa.”

“That’s the trouble,” said Hal.  “England has too many irons in the fire.  That’s where the Germans and Austrians have the edge, as we say in the United States.  Their armies are not scattered all over the world.”

“That’s true enough,” replied Colonel Anderson, “and it is, without doubt, the reason the Central Powers have not been crushed long ago.”

Ivan now took a hand in the conversation.

“These wonderful tales you told me of my brother Alexis,” he began.

“Well, what of them?” asked Hal.

“Why,” said Ivan.  “When I came with you I thought I should see some fighting.  All I have done is fly through the air, like a bird, and hear a thousand miles of talk.  I want to see some fighting, like Alexis saw.”

“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.”