"Here are the footprints of the rascals," announced Foster, as the two stepped cautiously into the bushes.
"Yes; there were just two of them here, apparently," replied Jack, after studying the prints, and discovering the marks of only two different sizes or kinds of shoes.
"Here's the imprint of a box," added Foster. "Good heavens, the scoundrels had a regular magneto battery, insulated wire and all, for firing that mine from the shore. Mr. Benson, they meant to blow your boat into Kingdom Come!"
"It looks that way," replied Jack Benson, composedly.
On hearing that voice, so even and unaffected in its utterance,
Lieutenant Foster looked at the submarine boy keenly.
"By Jove, Benson, you're cool enough to be an admiral," muttered the marine officer, admiringly.
"Why, this doesn't seem to be a joke on me," replied Captain, Jack, smiling back at the lieutenant.
"A joke!"
"It's one on the Secret Service," laughed Jack, quietly. "They are the ones who are supposed to have the job of keeping off spies and all of their kind."
"Yes; this certainly came from the spies, or their friends," muttered Lieutenant Foster. "Jove, but we have a desperate crowd to deal with when they'll go to such a length as this in time of peace!"