The sharp bark of a service revolver sounded.
"Crack! crack!"
Again and again the reports reverberated, and the water behind Herc grew troubled and crimson.
The fin vanished and only a small whirlpool remained to show where the mortally wounded shark had sunk slowly downward.
In the stern of the wherry stood Ned, his face set and stern, and in his hand the navy revolver that had done the work.
It was the ensign's weapon, which he had laid on the stern seat for his greater ease in moving about.
Ned, casting about for some means of saving Herc, had suddenly spied it, and, on the impulse of the moment, had snatched it up and fired.
"Well done, my lad," said the ensign in a voice that still trembled from the keen tension of the past few minutes.
"Sir—I——" began Ned, somewhat alarmed, now that Herc was out of danger. He had committed what he knew must be a breach of discipline in seizing the officer's pistol.
"You mean that it wasn't quite the thing to do to use my revolver," laughed the ensign. "My lad, I'm proud that it was put to such good service; glad that you were quick enough of wit to use it in the nick of time."