any number of deadly traps, into which they, in their ignorance, would surely stumble.
The three Air Service boys were still standing chatting with the girl in khaki, whom they knew very well, and sipping their lemonade when, without warning, there broke out a terrible din. The ground under their feet seemed to shake with the force of an explosion, which they realized must be quite near at hand.
Another explosion immediately followed, and then still more in irregular succession. The boys had learned by now to tell what such explosions signified, so they looked at each other aghast, and Jack cried out:
"The Huns are making an air raid on our lines back here! They must be in great force, too, with all those bombs dropping! Tom, didn't it strike you those explosions came mostly from the quarter where our Red Cross field hospital lies?"
Tom felt a cold chill, the same thought having gripped him.
