ered his escape.

All at once Mortlake, who was last, stumbled on a root and fell forward;
as he did so, his revolver was discharged twice. The shots rang out loudly
in the still night.

Instantly the light was extinguished. The next instant two dark figures
could be seen racing from the house. Before Lieut. Bradbury could call on
them to halt, they vanished in the darkness and a patch of woods to the
north.

"What a misfortune!" exclaimed Mortlake contritely, picking himself up.

Lieutenant Bradbury could hardly restrain his anger.

"How on earth did you happen to do that, Mortlake?" he snapped. "Those two
shots alarmed those rascals, and now they're gone for good. It's most
annoying."

"I appreciate your chagrin, my dear Bradbury," rejoined Mortlake suavely,
"but accidents will happen, you know."

"Yes, and sometimes they happen most opportunely," was the sharp reply.

Mortlake said nothing. In silence they approached the house, but nothing
save the pack of greasy cards, was found there to indicate the identity of
its late occupants.

There was nothing to do but to return to the automobile. They found old
Mr. Harding awaiting them eagerly. He showed no emotion on learning that
Roy's captors had escaped just as their capture seemed certain.

On the drive back to Sandy Beach, the old banker and Mortlake occupied the
front seat, while Roy and Lieut. Bradbury sat in the tonneau. As they
skimmed along, Roy drew something from his pocket and showed it to the
officer. It was an object that glistened in the wavering moonlight.

"It's a woman's hair comb!" cried the officer in amazement, as he regarded
it.

"Hush, not so loud," warned Roy. "I picked it up where I had the struggle
with the other Roy Prescott. It may prove a valuable clue."

CHAPTER XVI.

MISSING SIDE-COMB.

Some days after the strange and exciting events just recorded, Peggy burst
like a whirlwind into the little room,--half work-shop, half study,--in
which Roy was hard at work developing a problem in equilibrium. It was but
a short time now to the day on which they were to report to the navy Board
of Aviation at Hampton Roads, and submit their aerial craft to exhaustive
tests. Both brother and sister had occupied their time in working like
literal Trojans over the _Golden Butterfly_. But although every nut, bolt
and tiniest fairy-like turn-buckle on the craft was in perfect order, Roy
was still devoting the last moments to developing