"I don't know. I'll have to do a little investigating first. But he must be locked up. Schwen," went on the young inventor, "I'm sorry about this, but I shall have to give you into the custody of a United States marshal. You are not a naturalized citizen, are you?" The man muttered something in German to the effect that he was not naturalized and was glad of it. "Then you come under the head of an enemy alien," decided Tom, who understood what was said, "and will have to be interned. I had hoped to avoid this, but it seems it cannot be. I am sorry to lose you, but there are more important matters. Now let's get at the bottom of this." Schwen was, after a little delay, taken in charge by the proper officer, and then a search was made of his room, for, in common with some of the other workmen, he lived in a boarding house not far from the plant. There, by a perusal of his papers, enough was revealed to show Tom the danger he had escaped. "And yet I don't know that I have altogether escaped it," he said to Ned, as they talked it over. "There's no telling how long this spy work may have been going on. If he has discovered all the secrets of Shop Thirteen it may be a bad thing for the Allies and--" "Look out!" warned Ned, with a laugh. "You'll be saying things you don't want to, Tom and not at all in keeping with your former silence." "That's so," agreed the young inventor, with a sigh. "But if things go right I'll not have to keep silent much longer. I may be able to tell you everything." "Don't tell me--tell Mary," advised his chum. "She feels your silence more than I do. I know how such things are." "Well, I'll be able to tell her, too," decided Tom. "That is, if Schwen hasn't spoiled everything. Look here, Ned, these papers show he's been in correspondence with Blakeson and Grinder." "What about, Tom?" "I can't tell. The letters are evidently written in code, and I can't translate it offhand. But I'll make another attempt at it. And here's one from a person who signs himself Walter Simpson, but the writing is in German." "Walter Simpson!" cried Ned. "That's my friend of the tree!" "It is?" cried Tom. "Then things begin to fit themselves together. Simpson is a spy, and he was probably trying to communicate with Schwen. But the latter didn't get the information he wanted, or, if he did get it, he wasn't able to pass it on to the man in the tree. Eradicate nipped him just in time." And, so it seemed, the colored man had done. By accident he had discovered that Schwen had prevailed on one of the workmen in Shop 13 to change passes with him. This enabled the German spy to gain admittance to the secret place, which Tom thought was so well guarded. The man who let Schwen take the pass was in the game, too, it appeared, and he was also placed under arrest. But he was a mere tool in the pay of the others, and had no chance to gain valuable information.