Half a dozen times Frank left his two chums, sitting there killing time, to attend to something connected with the plane. He had carefully examined to find what had caused the accident that gave them such a thrill when thousands of feet above the earth.
"The same thing will never occur again, that I'm as sure of as I am of my own name," he told Billy, when the other asked him about it.
Several hours had passed since the soldier had left them. Pudge, having taken a stroll outside, came back to report that there were at least a dozen British "Tommies" standing guard around the enclosure in which the hangar had been erected.
"It's a good thing, too," said Pudge, "because a crowd has come out from town to hang around here in hopes we'll make a flight to-day. Oilskins and onions, but I should think there must be a hundred people if there's one. But those Tommies are ready to use their bayonets on the first fellow who tried to climb up and peep over the stockade."
"There are two guards, I noticed, down by the end of the trestle, where it strikes the water," observed Billy, who had been moving around.
Frank was doing some little job under the seaplane, and at this moment came sauntering toward his two mates. Billy, happening to glance up at the other's face was surprised to see that Frank looked excited; at least his eyes sparkled strangely, and there was a grimness in the way he had set his jaws.
Billy, always inclined to be explosive, might have burst out with a question only that he received a quick and expressive look from Frank, accompanied by the placing of a finger on his lips. Then, as Frank dropped into a chair beside them, Billy leaned over to whisper:
"What's up now, Frank, that you're looking so mysterious?"
"I've just made a discovery, that's all," came the same sort of careful reply. "Fact is, after all our precautions we've been outwitted, for there's a spy hidden in the hangar right now!"
"Are you joking, Frank?" asked Billy, though he should have known his comrade better than to believe Frank would try to play any silly trick for the sake of giving them a thrill.
Pudge opened his mouth, but for a wonder even one of his queer favorite expressions failed to drop from his lips. In fact, Pudge was rendered temporarily speechless by the astounding nature of Frank's communication.