"Yes, it was another warning," spoke the officer, "and one I hope you will heed. It concerns yourself, personally."
"Do you mean he is in danger?" asked Ned quickly.
"That's exactly what I do mean," was the prompt reply. "In danger of personal injury, if not something worse."
Tom did not seem as alarmed as he might reasonably have been under the circumstances.
"Danger, eh?" he repeated coolly. "On the part of whom?"
"That's just where I can't warn you," the officer replied. "I can only give you that hint, and beg of you to be careful."
"Do you mean you are not allowed to tell?" asked Ned.
"No, indeed; it isn't that!" the lieutenant hastened to assure the young man. "I would gladly tell, if I knew. But this plot, like the other one, directed against the inventions themselves, is so shrouded in mystery that I cannot get to the bottom of it.
"Our Secret Service men have been working on it for some time, not only in order to protect you, because of what you have done for the government, but because Uncle Sam wishes to protect his own property, especially the searchlight and the big cannon. But, though our agents have worked hard, they have not been able to get any clues that would put them on the right trail.
"So we can only warn you to be careful, and this I do in all earnestness. That was part of my errand in coming here, though, of course, I am anxious to inspect the new aerial warship you have constructed. So watch out for two things—your inventions, and, more than all, your life!"