“Turn it over,” said Bob.  “If it’s a real one given by the Kaiser it will have the recipient’s name on it.”

Sure enough, there it was: 

“Ober-Lieutenant Frederik von Arnheim.”

And beneath was inscribed: 

“Pour le merite.”

“Great Scott, Bob,” said Frank.  “What do you make of this?”

“Some Hun officer stole our airplane,” said Bob.  “That’s what I make of it.”

“But the war is over,” protested Frank.

“Maybe it is,” said Bob darkly.  “But if that bird doesn’t fly back with our airplane I’ll make war on Germany myself.”

Despite his gloom, Frank grinned.  He slapped big Bob on the back.  “Come on, old boy,” he said.  “No use hanging around here.  We may as well go back to the house and report the latest mystery.”

“I wonder,” said Bob, as they set out, “whether there is any connection between the two—­between this theft of our airplane and that stuff yesterday.”

It was Mr. Temple who was able to provide an answer to that question.  The boys found him up and dressed when they reached home, and himself considerably excited over a telephone call from New York City.  He, too, was dismayed when told of the theft of the airplane.  But when the boys showed him the German Iron Cross he hit the desk before him a resounding blow with his fist.  Their conversation took place in the library.

“That fits right into the puzzle,” said he.  “Boys, while you were out of the house I had a long distance telephone call from New York City.  The man who called said he was a chauffeur who had driven two men down here yesterday, that he thought they were on legitimate business, but that when Bob tried to stop them he saw they were bad ones, as he put it.  Later, when they made him drive them over to the radiophone station and he heard Tom rout them with his pistol shots, he said he drove off as they ran for his car and left them.  He inquired in the village and learned my name, and so called me up to clear himself in case I intended starting a pursuit.

“And he said,” added Mr. Temple, leaning forward and speaking impressively, “that he was pretty certain one man was a Greaser and the other a Hun.  Those were his own words.  Of course, he meant one was a Mexican and the other a German.”

“So when this chauffeur abandoned them they stole our airplane to get away,” cried Frank excitedly.

“Exactly.”

“Maybe,” said Bob, “I copped every cent they had in pulling that Mexican’s coat off his back, and they were without carfare back to the city.”

“Oh, I suppose the German had money,” said his father.  “The German probably was an aviator.  And they stole the airplane in order to escape from here quickly before we could get in pursuit of them.  I imagine they’ll land in some deserted spot—­plenty of them in the sandy reaches along the New Jersey coast, for instance—­make their way to a railroad, after abandoning the plane, and go——­”