ough the dark
tunnels where they could hear the sea booming close overhead, and could
hear the wild pursuit behind.

Their feet slipped on the damp floor and they crashed into the walls of
the tunnel at the turns. The pursuit was closer behind--as they started
climbing the last passages to the water-cavern, the torchlight behind
showed them to their pursuers and wild yells came to their ears.

They had before them only the last ascent to the water-cavern when Ennis
stumbled and went down. He swayed up a little, yelled to Campbell. "Go
on--get Ruth out! I'll try to hold them back a moment!"

"No!" rasped Campbell. "There's another way--one that may mean the end
for us too, but our only chance!"

The inspector thrust his hand into his pocket, snatched out his big,
old-fashioned gold watch.

He tore it from its chain, turned the stem of it twice around. Then he
hurled it back down the tunnel with all his force.

"Quick--out of the tunnels now or we'll die right here!" he yelled.

They lunged forward, Campbell dragging both the girl and the exhausted
Ennis, and emerged a moment later into the great water-cavern. It was
now lit only by the searchlight of their waiting cutter.

As they emerged into the cavern, they were thrown flat on the rock ledge
by a violent movement of it under them. An awful detonation and
thunderous crashing of falling rock smote their ears.

Following that first tremendous crash, giant rumbling of collapsing rock
shook the water-cavern.

"To the cutter!" Campbell cried. "That watch of mine was filled with the
most concentrated high-explosive known, and it's blown up the tunnels.
Now it's touched off more collapses and all these caverns and passages
will fall in on us at any moment!"

The awful rumbling and crashing of collapsing rock masses was deafening
in their ears as they lurched toward the cutter. Great chunks of rock
were falling from the cavern roof into the water.

* * * * *

Sturt, white-faced but asking no questions, had the motor of the cutter
running, and helped them pull the unconscious girl aboard.

"Out of the tunnel at once!" Campbell ordered. "Full speed!"

They roared down the water-tunnel at crazy velocity, the searchlight
beam stabbing ahead. The tide had reached flood and turned, increasing
the speed with which they dashed through the tunnel.

Masses of rock fell with loud splashes behind them, and all around them
was still the omi