“I’m not such weak stuff as that, sir,” almost grumbled the machinist.  “I can stand a few minutes more in wet clothes, and I want to go along to see where this wire leads.”

“Good enough,” nodded Lieutenant Foster, he gave the order to row along slowly, while two marines in the bow of the cutter slowly gathered in the wire, at the same time signaling back the direction in which it lay.

Only a few minutes were needed thus to follow the trail straight to the clump of bushes on shore.

“Nobody leave the boat until we have a lantern ready,” directed Lieutenant Foster.  “We don’t want to tramp out the trail of the rascals who laid that mine.”

The marine lieutenant himself was the first to step ashore, and Jack Benson was with him.

“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!”

“Oh, it may all turn out to be a joke,” put Hal, quietly.  “Some one may have been doing this to try us out.  That metal cylinder may prove to have been loaded with ginger-bread or peanuts.  If anyone has been trying a joke on us, then I’m mighty glad we didn’t get rattled.”

“I reckon we shall soon know just what that cylinder did contain,” muttered Lieutenant Foster.  “Here’s another cutter coming from the ‘Waverly,’ and I think I make out Lieutenant Commander Kimball in the stern-sheets.”

It was, indeed, the lieutenant commander.  As he stepped ashore, his face coming into the circle of light cast by the lantern, his features were seen to be white with anxiety.

“We have just looked into the cylinder,” he announced, in a low voice.  “We found there enough gun-cotton to blow the ‘Benson’ into inch pieces.  It was a fearful crime to plan.”