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?" "Lieutenant Mackinson," the message began to come back. "Locked in closet off engine room. Can't make self heard. Can you help?" "This is Slim," the youth rapped back upon the pipe. "Caught your message on deck. Am coming with help at once." And he dashed down the deck toward the captain's quarters, almost bowling over the captain's aide as he hurtled into the sanctum of the ship's commander unannounced. "Well?" the captain demanded sternly. "Why all the haste?" "Lieutenant Mackinson," Slim blurted out; "he's locked in a closet down near the engine room." "Locked in a closet!" the captain repeated incredulously. "How do you know?" "He gave a telegraphic call for help on the steam-pipe which runs through there and connects with the whistle," the lad explained. "I was on deck and heard it. I talked with him over the pipe." "There is no time to lose, then. Come with me." And the captain himself hurriedly led the way down through the lower depths of the ship, where it became hotter and more oppressive with every step they took. They had taken a route by which they escaped the attention of anyone else on the ship. "It should be right about here somewhere," the captain announced, as they approached a particularly dark passage. For a few steps they felt their way along, and then stopped to listen. There was nothing but the dull and constant hum of the engines and the almost insufferable heat.