“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 the balancing device to which he mainly pinned his hopes of besting the other craft.

From the newspapers they had been made aware that several types, bi-planes, monoplanes and freak designs were to compete, and Roy was not the boy to let lack of preparation stand in the way of success.  Detectives and the local police had been set to work on the mysterious plot whose object had been to entrap the boy.  But no result had come of their work.  Incidentally, it had been found, when the auto which Roy had driven to the deserted house was towed back for repairs, that the tank had been punctured by some sharp instrument.

As for the clue of the brilliant-studded comb, Peggy on examining it, declared it to be one of a pair of side-combs, which only complicated the mystery.  Roy had thought of surrendering this clue to the police, but on thinking it over he decided not to.  He had an idea in regard to that comb himself, and so had Peggy, but it seemed too wild and preposterous a theory to submit to the intensely practical police of Sandy Beach.

Roy looked up from the paper-littered desk as Peggy flung breathlessly into his sanctum.  He knew that only unusual news would have led her to interrupt his work in which she was as keenly interested as he was.

“What is it, Sis?” he asked, “you look as excited as if the Statue of Liberty had paid us a visit and was now doing a song and dance on the front lawn.”

“Oh, Roy, do be serious.  Listen—­who do you suppose has come back to Sandy Beach?”

“Not the least idea.  Who?”

“Fanning Harding!”

“Fan Harding!  The dickens!”

“Isn’t it, and more than that, he is down at the Mortlake plant now.  He is going to take up the Cobweb.  And who do you think is to be his companion?”

“Give it up.”

“Regina Mortlake!”

“Phew!” whistled the boy, “a new conquest for the irresistible Fanning, eh?”

“Don’t be stupid,” reproved Peggy, severely, “I’ve been thinking it over and I’ve just hit on the solution.  Fanning, or so I heard, took up aviation when he was in the west.  You know he always had a hankering for it.”