"Well?" asked Tom suggestively.
"I was going to say if only those foreign spies don't make trouble."
"I think we've seen the last of them," Tom declared. "Now we'll go on with the tests."
More guns were fired, singly and in batteries, and in each case the Mars stood the test perfectly. The double barrel had solved the recoil problem.
For some little time longer they remained out over the sea, going through some evolutions to test the rudder control, and then as their present object had been accomplished Tom gave orders to head back to Shopton, which place was reached in due time.
"Well, Tom, how was it?" asked Mr. Swift, for though his son had said nothing to his friends about the prospective test, the aged inventor knew about it.
"Successful, Dad, in every particular."
"That's good. I didn't think you could do it. But you did. I tell you it isn't much that can get the best of a Swift!" exclaimed the aged man proudly. "Oh, by the way, Tom, here's a telegram that came while you were gone," and he handed his son the yellow envelope.
Tom ripped it open with a single gesture, and in a flash his eyes took in the words. He read:
"Look out for spies during trial flights."