led at the unexpected sound.

"Loose board, I guess," replied Jimmie, rather disgruntled at the turn
affairs had taken. "The wind's ripping everything loose!"

Again the tapping was repeated in an insistent manner.

"I'm going to see what's going on here!" declared Ned, rising from his
position. "Some one is trying to communicate with us!"

"Some bloomin' Dutchman's tryin' to ask us whether we want sausage with
our pancakes for breakfast!" growled Jimmie. "Let 'em alone!"

Disregarding this statement the older lad proceeded toward the window,
where fitful gusts of sleet beat. Outside the darkness covered
everything. Only an occasional point of light indicated a sentry hut.

"Who's there?" demanded Ned in a low tone.

"Sh-h-h!" came a hiss from the darkness. "Open the window!"

Ned fumbled a moment at the fastening. Presently he found the catch
sliding the sash back in its channel. An exclamation escaped him as he
did so. The face of the visitor was none other than that of their missing
acquaintance, Mackinder. Ned was astounded.

"Thought you were dead!" he cried in amazement.

"Hush!" cautioned the other. "Not so loud. Now, if you lads want to get
out of here this is your time. Everybody's busy or asleep!"

"How do you know we want to get out of here?" demanded Jimmie in a low
tone as he approached the opening.

"Don't you suppose I have eyes? I saw what you were up to!"

"Oh, you did, eh? Then what do you want us to do?"

"If you want to get away from this place according to your plan, now is
the time to take action," replied Mackinder in a whisper. "If you prefer
to wait until tomorrow and stand trial for an offense of which you are
innocent I cannot offer any objection of course."

"Ned, I think we'd better make our getaway while the going's good!"

"Second the motion!" declared Harry, who had softly approached the
window. "Let's make a noise like a drum!"

"I'm with you!" stated Frank, raising a foot to the window sill.

"Easy there!" cautioned Jimmie. "Mind your step!"

Frank was through the window in an instant. He landed on the earth with
Mackinder's assistance without noise. Quickly the others followed. Ned
took the precaution to slide the window shut.

Cautiously the little group of six made their way in the direction of the
wharf where the submarines were moored. Mackinder took the lead as if
familiar with the ground. Once he paused, extending a warning hand to
Jimmie, who was directly b