lf, 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?"

"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 lock