in this
horrible fog. And that might mean--they shivered and turned dismayed
faces to each other.

"I--oh, I'm awfully sorry," wailed Laura. "If I hadn't said what I did to
Paul we might never have come."

"Nonsense! that had nothing to do with it," said Billie, putting a loyal
arm about her chum. "We would have come just the same."

Then followed a waking nightmare for the boys and girls. In a few moments
the fog settled down upon them in a thick impenetrable veil, so dense
that, as Paul had said, you could almost have cut it.

It became impossible for Paul to steer, and all there was to do was to
sit still and wait and hope for the best. Fog horns were sounding all
about, some seeming so close that the girls fully expected to see some
great shape loom up through the mist, bearing down upon them.

For a long time nobody spoke--they were too busy listening to the weird
meanings of the fog horns and wondering how they could have escaped a
collision so long. For a while Paul had kept the engine running in the
hope that he might be able to keep to his course and eventually get to
Lighthouse Island. But he had decided that this only made a collision
more likely, and so had shut it off. And now they had been floating for
what seemed hours to the miserable boys and girls.

It was Connie who finally broke the silence.

"Oh, dear," she said, apropos of nothing at all, "now I suppose we'll
have to die and never solve our mystery after all." She sighed
plaintively, and the girls had a wild desire to shout with laughter and
cry at the same time.

"Goodness," said Laura hysterically, "if we've got to die who cares about
mysteries anyway?"

The boys, who had been peering ahead into the heavy unfriendly fog,
looked at the girls in surprise.

"What do you mean--mystery?" Ferd asked.

Before the girls could answer a sharp cry from Paul jerked their eyes
back to him.

"Look!" he cried, one hand on the wheel and the other pointing excitedly
before them to a dark something which loomed suddenly out of the mist.
"There! To starboard. We'll bump it sure!"

CHAPTER XXI

THE BOYS ARE INTERESTED

For a moment the girls were too terrified to speak. And the next moment
they could not have spoken if they had wanted to, for _The Shelling_
collided so suddenly with whatever it was that had risen out of the mist
that they had all they could do to keep from being thro