nous grinding of mighty weights of rock. The walls of
the tunnel quivered repeatedly.

Sturt suddenly reversed the propellers, but in spite of his action the
cutter smashed a moment later into a solid rock wall. It was a mass of
rock forming an unbroken barrier across the water-tunnel, extending
beneath the surface of the water.

"We're trapped!" cried Sturt. "A mass of the rock has settled here and
blocked the tunnel."

"It can't be completely blocked!" Campbell exclaimed. "See, the tide
still runs out beneath it. Our one chance is to swim out under the
blocking mass of rock, before the whole cliff gives way!"

"But there's no telling how far the block may extend----" Sturt cried.

Then as Campbell and Ennis stripped off their coats and shoes, he
followed their example. The rumble of grinding rock around them was now
continuous and nerve-shattering.

Campbell helped Ennis lower Ruth's unconscious form into the water.

"Keep your hand over her nose and mouth!" cried the inspector. "Come on,
now!"

Sturt went first, his face pale in the searchlight beam as he dived
under the rock mass. The tidal current carried him out of sight in a
moment.

Then, holding the girl between them, and with Ennis' hand covering her
mouth and nostrils, the other two dived. Down through the cold waters
they shot, and then the swift current was carrying them forward like a
mill-race, their bodies bumping and scraping against the rock mass
overhead.

Ennis' lungs began to burn, his brain to reel, as they rushed on in the
waters, still holding the girl tightly. They struck solid rock, a wall
across their way. The current sucked them downward, to a small opening
at the bottom. They wedged in it, struggled fiercely, then tore through
it. They rose on the other side of it into pure air. They were in the
darkness, floating in the tunnel beyond the block, the current carrying
them swiftly onward.

The walls were shaking and roaring frightfully about them as they were
borne round the turns of the tunnel. Then they saw ahead of them a
circle of dim light, pricked with white stars.

The current bore them out into that starlight, into the open sea. Before
them in the water floated Sturt, and they swam with him out from the
shaking, grinding cliffs.

The girl stirred a little in Ennis' grasp, and he saw in the starlight
that her face was no longer dazed.

"Paul----" she muttered, clinging close to Ennis in the water.

"She's coming back