Nevertheless, neither the excitement nor the potential danger of the situation was sufficient to prevent Jerry and Slim from taking a full eight hours of much-needed sleep, while Lieutenant Mackinson, Joe and three other officers whom the captain had taken into his confidence in the matter, followed out every possible clue in pursuit of a solution of the baffling mystery.
The record of every enlisted man and officer on the vessel had been most carefully probed, without building up enough suspicion to warrant the singling out of any individual as the probable offender.
Likewise an investigation of the members of the crew had failed to develop anything tangible, even directly suspicious. It was a case of watch everybody, take every precaution, and be prepared for anything. Only nine men on the vessel, however, including the spy himself, knew anything about it, and the rest were in utter ignorance of the treachery that might be directed against them at any time.
Refreshed by their sleep, Jerry and Slim arose about four o'clock that afternoon. Joe, who had rested easily throughout the later excitement of the preceding night, was still in the midst of the investigation and was not then to be found. Jerry had some letters to write, so Slim went to the upper deck alone.
Seeing no one that he knew, and his mind weighted anyway with the menacing mystery of the strange happenings of the night before, he sat down on a coil of rope, just in the lee of the forward smokestack, to think the whole matter over for the twentieth time.
He was thus absorbed when something, at first vague and indefinite, then clearer and clearer until it was unmistakable, began to impress itself upon his mind. Like the awakening call that comes to a man in a sound sleep—seemingly as a far-off whisper that gradually gathers volume and strength until finally the sleeper awakes with a start to find someone standing directly over him, loudly and insistently calling his name—so Slim came to a realization of the strange series of sounds that were being repeated within a few feet of him.
Could it possibly be only the crackling of the steam-pipe that ran along the smokestack to the whistle—a crackling merely from the pressure within? For a moment Slim thought an over-wrought imagination was playing tricks upon him. But he rose hastily and crossed the short intervening distance.
Clearly and distinctly it came to him then. Someone in another part of the vessel was rapping desperately upon that pipe! And in the long and short dashes of the international code that someone was repeating a single word—"Help! Help! Help!"
In another instant, using the heavy end of his jackknife as a crude transmitter, Slim was tapping off the reply:
"Who are you—and where?"