"How do you know?"
"I saw him. He pretended to be looking at the carte de jour, and I caught a glimpse of a sheet of paper on which he was making certain marks. I'm sure he was sketching out something about the railroad, for use, maybe, in a future air raid."
"Nonsense!" exclaimed Tom. "As a matter of fact, I don't doubt that the German secret agents know every foot of ground in and about Paris. They must have maps of this railroad the same as the French have of some of Germany's, only you've got to hand it to the Huns! They certainly went into this thing well prepared the more discredit to us, in a way. But are you sure of what you say, Jack?" he added, after a moment's thought.
"Positive! I'm sure that man is a German spy, masking as a Hollander or possibly a Swiss. He's sighing for some of his country's good cooking—though that's one of the few good things about it—and he's making some sort of a map."
Tom thought over the matter a moment. The man did not appear to notice the two chums.
"I'll tell you what we can do," Tom said. "We'll soon be in at the Gare de l'Est, and we can tip off some of the officers around there. They can follow this fellow, if they think it's worth while."
"Well, I think it's worth while," said Jack. "If that fellow isn't a spy I'm a Dutchman!"
As Jack spoke the man looked up and full at the two lads, almost as if he had heard the words.