"Hang on tight!" shouted Hal. "You never can tell what will happen with me running this thing, so don't take any chances."
"I'll hang on tight in the future, never fear," was the reply. "What do you suppose that shot was?"
"Some sentry, I suppose. I guess he knew no machine was supposed to be flying around here. That's probably why he took a shot at us. We were flying too low, anyhow. We will stay up here, where we can't be so easily seen or heard."
For some time the boys sailed along without a word, and then, just as Chester opened his mouth to ask Hal where he supposed they were, there was the sound of rushing wings, and, turning in his seat, Chester beheld a huge shape rushing after them.
"Speed up, Hal!" cried Chester. "We are pursued!"
Without stopping to ask questions, Hal threw the speed lever over, and the machine leaped forward like some live thing.
At the same moment there came the crack of a rifle, and, as Hal dropped one arm from the steering wheel the aeroplane rocked crazily and dived toward the ground.
The bullet had grazed Hal's left shoulder.
With a desperate effort, the lad righted the machine with his one good arm, and it shot upward again.
"What's the matter?" gasped Chester. "Are you hurt?"