“Hm-m-m,” muttered the officer.  “Why didn’t the ambassador make use of the wireless ’phone?”

“I don’t know, sir,” replied Chester.

The officer laid a heavy hand on the lad’s arm, and peered into his face in the dim light.  Then the hand tightened.

“You are no German!” was his quiet comment.  “You are probably a spy.  You are my prisoner!”

Chester’s heart sank.

CHAPTER XVI.

A friend in need.

Many thoughts ran through Chester’s head as he stood there for a brief moment with the hand of the man who had accosted him on his shoulder.  He thought of flight and he thought of fight, but most of all he thought of the ill fortune he had encountered in the past few days.

“This is the limit,” he told himself ruefully.  Aloud he said:  “You are mistaken, sir.”

“No, I’m not mistaken,” returned the officer, “and I suppose most would take you at your word.  You speak German without an accent, but your face betrays you.  At a guess, I would say you are English.”

“You are wrong,” declared Chester.

“Nevertheless, I shall have to ask you to accompany me,” said the officer.

For a moment Chester hesitated; he was tempted to leap upon his captor and make a fight for it, but he had hesitated too long now.  The officer produced a revolver, which he held carelessly in his right hand.

“I have a little persuader here, in case you should think of disobeying my order,” he said quietly.

“Oh, all right,” said Chester.  “I’ll go along.”

“I thought you would,” replied his captor, with a smile.

He motioned for Chester to walk on ahead of him, which the boy did, the while grumbling to himself.

“I should have run when I saw him coming,” he muttered.

There was little doubt in Chester’s mind now that he was due for his trip to Vienna with the ambassador.  After that, in view of his attempt to escape, he wasn’t sure what might happen, for he believed the ambassador would recall his offer of a safe conduct after this.

“Yes, it looks like Vienna to me,” he told himself.

And so it probably would have been but for one thing—­or rather, for one person; and Chester had no more idea of seeing him than he had of encountering Hal at the next cross street.

As the two walked along, Chester slightly in front, his captor following him closely with drawn revolver, a figure left the shadow of a nearby building, and with a whistle of amazement, crept silently in their wake.

“Well!  Well!” muttered this figure to himself.  “What do you think of that?  I can’t stand for this.  I’m liable to get killed or hurt, but I’ve just got to take a hand.”

As Chester and his captor turned into another street and disappeared from sight, the man broke into a run, stepping lightly on his toes.  When he rounded the corner he was only a few feet behind the other two.  Silently as a cat, he closed up the distance, drawing a weapon from his pocket as he ran.