"Sort of," admitted Bob. "Fritz tried to put one over on us."
"Yes, we heard about it," went on Gerald. "And it came near being a bigger thing than you fellows suspect. Did you hear about the smoke signals?"
"Smoke signals?" cried Jimmy. "Say, do you mean that there has been some more of that traitorous work going on?"
"It looks so," said John. "When we were out flying around yesterday we passed over a little valley. We were low enough down to see four men around a queer kind of machine. At first we thought it was a hidden mortar battery, but soon we saw some green and yellow puffs of smoke go up from it. We reported the matter to headquarters, and there was an investigation right off, but the four men had disappeared with their smoke apparatus when a squad of our lads got to the valley."
"Do you say there were four men around that smoke signaling apparatus?" asked Jimmy.
"Yes," answered Gerald.
"Could you tell who they were?"
"Well, no, not exactly. Except that two of them seemed to be men in American uniforms, and the other two were civilians."
"By Archibald Montmorency! as our cook would say," cried Jimmy, "I'll bet they're the same fellows we saw in the dugout. They are the traitors! This is great news you bring from the air, boys!" he said to the Twinkle Twins.
Wonderingly the four gazed at one another.