Dave sat a long time in thought.  At last he decided what to do.

“Perhaps you’re right, Jarvis,” he said finally, rising.  “But our first job is the Pole.  The shaft must be nearly fitted by now.  Let’s see how they’re coming.  Perhaps we’ll be away in the morning.”

As they rounded a block of ice by the shore, Jarvis gave a start and seized his companion by the arm.

“D’y’ see ’im?” he whispered “‘E was starin’ h’at us from behint them ice-piles.  ’E was a Jap.  I’ll swear it.”

“Aw, you’re seeing Japs to-night,” laughed Dave.

“Ow is she?” Jarvis asked of a gob whom they met.

“Right as they make ’em—­now.  But I’ll say it was some job that.  The shaft was twisted something awful—­like a corkscrew.  But it was some steel, that shaft, and we just het her up an’ twisted her straight again.  The Doc said he guessed it would be a bit short, but when we got her back in place she fitted like paint.  Then we slid the old boat back in the water and tried her out and she runs like a watch.”

“Grand.  We’re off in the mornin’.”

Dave and Jarvis turned to make their way to the submarine where a single gob, pacing the white ice-surface, had laughed at his job of watching natives who could not be induced to come within a half-mile of him.

Suddenly the engineer jumped forward.

“Did y’ see that?” Jarvis grabbed Dave by the arm and urged him into a run. “’E went down—­the guard, I saw ’im,” panted Jarvis.  “I saw ’im, then h’I didn’t.  H’it’s the Japs.  Listen!”

There came distinctly the sound of a dragging hawser.

“H’it’s the Japs; the blooming bloody ’eathen,” Jarvis panted.  “They’re h’after the submarine!”

Dave dragged him behind an ice-covered boulder.

“Quick!” he whispered.  “If the submarine goes, we go with her, inside or outside, somewhere.  We’ve got to take the chance.”

Darting from ice-pile to ice-pile, they soon reached the water’s edge.  There lay the guard, unconscious, an ugly bruise on the side of his head.  And there lay the submarine, silent and closed.

“She’s off!” breathed the engineer.

It was true.  The craft already showed a line of dark water between her and the shore.

Without hesitation, the old engineer sprang upon her deck and crouched by the conning-tower.  Instantly Dave followed him.  Their soft skin-boots made no sound.  And, as they crouched there, the submarine headed for the channel and then toward the west.

“To the treasure city, h’I’ll be bound,” whispered Jarvis.

CHAPTER XI

A BATTLE BENEATH THE ARCTIC MOON

“The treasure city”

“We’ll stick ‘ere behint th’ connin’-tower,” the engineer explained to Dave, as the submarine, turning, put off up the dark channel which separated the solid shore-ice from the great drift of ice-floe that lay beyond.