"Wouldn't you like to go up with me to-morrow, Chester?" asked Fritz, as he locked the door to the shop.

"I believe I would," was the reply. "I guess I can stand it if Hal can."

"Then you shall," said Fritz, and the three turned toward the house, where Frau Schmidt stood in the doorway, calling to them that supper was ready.

CHAPTER X.

IN THE AIR.

The boys were busily engaged in disposing of a hearty supper when there came a knock at the door. Frau Schmidt answered the knock, and, returning a few moments later, placed before Hal an important-looking letter, bearing the official seal of the German government.

Hal opened the doc.u.ment and read.

"Great Scott!" he exploded, after a hasty perusal.

"What's the matter?" demanded Chester anxiously.

"Why, here is an order, commanding us to report to the commanding officer the first thing in the morning, so that we may be transported back to Berlin!"

"Berlin! What in the world do we want to go back to Berlin for?"

"We don't; but it looks as though there were no help for it. The letter says that, after an investigation of our case, it has been decided that we shall be sent back to Berlin and that, if we are to be allowed to leave the country, such arrangements must be made by the United States amba.s.sador."

"Well, what do you think of that!"

"It's too bad," declared Fritz; "but an order is an order. I am afraid you must go!"

"You poor boys!" exclaimed Frau Schmidt "I can't see why they won't let you stay here."

"No more do I," declared Hal. "But I guess this letter means business."

"It sure looks like it," said Chester.

"That's what I call pretty tough luck," declared Hal, when the two boys were alone in their room that night, Fritz and his mother having retired.

"Tough? I should say it is tough," returned Chester. "After all the trouble we have had getting away from Berlin, then to have to go back.

Tough is no name for it."

"Well," said Hal, "I guess there is no use kicking. We ran a good race, but we lost. It's back to Berlin for us."

Suddenly Chester sat bolt upright

"By George!" he exclaimed.

"What's the matter now?" asked Hal in surprise.

"I've an idea."

"Strange," replied Hal, with a smile; "but let's hear it."

"Well, in the first place, you took an airship ride to-day. How did you like it?"

"Like it? Oh, I liked it all right. Why?"

"You saw Fritz work the thing. Did you get the hang of it?"

Hal jumped to his feet with a subdued exclamation.

"I see what you are getting at!" he declared. "An airship! Why didn't I think of it myself?"

"There are only two objections I can see to the plan," said Chester.

"What are they?"

"Well, the first is, can you run the thing without spilling us out?"

"I am willing to take a chance if you are. Fritz explained the workings of the machine while we were aloft to-day. I am sure I can do it. What is the second reason?"

"The second reason is that it seems a shabby trick to play on Fritz, particularly after the way he has treated us."

"So it does," agreed Hal slowly, but, after a pause, he added: "However, I believe we had better do it. To me it looks like the survival of the fittest."

For a long time the boys debated this point, but the matter was finally settled when Hal said:

"Well, if we don't, we are likely to be stuck in Germany until the war is over; and there is no telling when that will be."

"As long as we are going to do it, then," returned Chester, "the sooner we start the better."

"Right," replied Hal. "Let's get busy."

"How are we to get the aeroplane out of the shop? You know the door is locked."

"Yes, but I know something else, too. I noticed it to-day, and wondered why those men who came after the key didn't take advantage of it."

"What is it?"

"The bolts in the hinges of the door can be lifted out easily, and we can take the doors off."

"But we must get rid of the two soldiers who keep guard at night."

"We will do that some way, all right."

"Come on, then; let's get started."