“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.”

“Such is not the plan of the general staff.  Their reasons I cannot tell you; but at a guess I should say it is because they hope that, by a juncture with the Anglo-French forces, they may hope to show an effective front until Italy can throw an army to their support, or possibly until the long expected Russian offensive materializes.”

“Then we shall have to bring some pressure to bear upon Greece,” said the younger man.  “We cannot permit that.  Bulgaria must get in the game sooner and thus foil such a plan.”

“Well, you probably know best,” said the officer, “but remember one thing.  To all intents and purposes, Bulgaria is still neutral.  Announcement that she has decided to cast her lot with the Central Powers, if premature, undoubtedly would spoil many plans.  Particularly, if it came to the ears of the Anglo-French commander at Saloniki.”

“Exactly,” replied the young man.  “Our plans now are to permit the Allies to advance a considerable distance toward Belgrade, and then to have Bulgaria declare war at the psychological moment.”

“A good plan, that,” returned the officer.  “But I must get back now.  My absence will be noticed and I do not care to arouse suspicion.”

The men moved off.

Chester and Colonel Anderson gazed at each other.

“Rather neat little play,” said Colonel Anderson.

“Rather,” repeated Chester dryly.

“And to think,” continued Colonel Anderson, “how leniently Bulgaria has been treated by the Allies.  Well, her day of reckoning will come.”

“We’ll have to get word of this to the Serbian commander in Belgrade,” said Chester.

“So we will,” said the colonel.  “And also to the commander of the Anglo-French forces in Saloniki.”

“Let’s get back then and see if Hal has the machine fixed so she’ll fly.”