"Did you come on from Washington yesterday?" asked Tom, as he,
Ned and the officer strolled toward the shed where was housed the
aerial warship.

"Yes, and I spent the night in New York. I arrived in town a
short time ago, and came right on out here. At your house I was
told you were over in the fields conducting experiments, so I
came on here."

"Glad you did," Tom said. "I'll soon have something to show
you, I hope. But I am interested in hearing the details of this
suspected plot. Are you sure one exists?"

"Perfectly sure," was the answer. "We don't know all the
details yet, nor who are concerned in it, but we are working on
the case. The Secret Service has several agents in the field.

"We are convinced in Washington," went on Lieutenant Marbury,
when he, Tom and Ned were seated in the private office, "that
foreign spies are at work against you and against our
government."

"Why against me?" asked Tom, in wonder.

"Because of the inventions you have perfected and turned over
to Uncle Sam--notably the giant cannon, which rivals anything
foreign European powers have, and the great searchlight, which
proved so effective against the border smugglers. The success of
those two alone, to say nothing of your submarine, has not only
made foreign nations jealous, but they fear you--and us," the