"Tell us about yourself," said Alfred. "How did you happen to lose your right arm?" "Tried to bring down too many of them in one day, I suppose. Oh, they gave me a tough fight; but they came down when I did." "So you are not flying now?" remarked Alfred with a rueful voice. "No," said Joe, looking down and slowly shaking his head. "I can do it as well as ever, but they won't let me." "See here, Joe; we've got something that's bothering us; we believe we are on the trail of a spy. He acts like it. It's a peddler. I followed him around, and both of us noticed some suspicious-looking things on his part," said Ralph. "A peddler!" remarked Joe. "Why, I saw a peddler around here a half hour ago. Fellows of that kind need watching. Go on investigating. I am awfully sorry I can't move around as I used to, or I would help you out." "What is the matter with your foot?" asked Alfred, as he now saw a bandage above the ankle. "Oh, that was only a part of the damage. Go on, boys; see the commandant; here, let me give you a note; now, take it over to that low building in front of the brown warehouse," said Joe. "Thank you for the hint," said Alfred. "Don't forget to come back; I want to talk with you," remarked Joe, as he waved his hand in the parting salute. The peddler was nowhere to be seen as they hurried across the field. The boys were too much excited to open and read the note which Joe had given them. "Is the commandant in?" asked Alfred, as they approached the guard. An orderly appeared, and to him Ralph handed the note. It was at once taken into the officer's room. The orderly came out smiling, bowed and said: "Col. Winston wishes you to step in." They were met at the door by the officer, who grasped their hands warmly as he said: "You don't know how happy I am to meet you. My brother always speaks so affectionately of you, and my sister is really much hurt because you left Dunkirk without seeing her." The boys were astonished. Ralph was the first to speak: "Are you Lieutenant Winston's brother?" "Did he recover from the fall in the airship?" asked Alfred. "Yes, and he says that without you he would have been crushed to death; we are certainly thankful to you. And now, what can I do for you? Joe says you have something important to communicate to me without delay," said the colonel, glancing at the note. "We may be mistaken," said Ralph, "but we think we have spotted a spy." "Where?" asked the colonel, as he arose from the chair. "Here in the camp?" "Yes, right here; over in the warehouse and at the hangars, and he acted so suspiciously before he reached the camp that we've been trailing him," said Alfred. The colonel tapped a bell. The orderly appeared. "Send for Captain Rose. Tell him it is urgent," said the colonel. "We ought to be out looking for the fellow, for we missed him as we came across the grounds. He's a peddler," said Ralph.