“All right,” assented Fanning, rather sullenly, “if you insist; but I think we ought to hurry back at once.”

“By all means,” quoth the bland Jimsy, “but—­hullo, what’s this!” He was stooping over the wheels now.  “This wheel has been tampered with.  The holding cap must have been partially unscrewed.  Look here!”

He held up the brass cap which was supposed to keep the wheel on its axle.

“Some of the threads have been filed out of this,” he said positively.

“Let’s have a look,” said Fanning eagerly.  He leaned over and scrutinized the part which Jimsy was examining.

“Those threads haven’t been filed,” he said, “they’ve worn.  Very careless not to have noticed that.  It’s surprising that it held on so long.”

“It might have held for a year if the car was run at average speed,” said Jimsy slowly, “but the minute it was raced beyond its normal rate the weak part would have gone.”

“What do you mean to imply?” blustered Fanning, though his face was pale and his breath came quickly.

“I don’t imply anything,” said Jimsy slowly, “but I’d like to know who filed this cap down.”

“Pshaw!  You are dreaming,” scoffed Fanning.

A dull flush overspread Jimsy’s ordinarily placid face.

“After a while I’ll wake up, maybe,” he said, “and then——.”  He stopped.

“Well, let’s see about getting Roy home,” he said, “Peggy, you can drive the Blue Bird and Fanning and Miss Mortlake can sit in the other machine as soon as we get the wheel back.  Then Jess and I will go ahead in the Red Dragon Fly and break the news to Miss Prescott.”

Shortly thereafter the two autos moved slowly off, while the aeroplane raced above them, going at a far faster speed.

Regina turned to Fanning.

“Do you think that odious boy suspects anything?” she asked.

“I guess he does.  But he can’t prove a thing, so that’s all the good it will do him,” scoffed Fanning, “and besides, if they get too gay we’ve got a marked bill that will make it very unpleasant for a certain young aviator.”

CHAPTER XVIII.

A BOLT PROM THE BLUE.

The broken ankle which both Peggy and Roy had dreaded, turned out to be only a sprain—­affecting the same unlucky ankle that had been injured on the desert.  This was a big relief, as a broken joint would have kept Roy effectually out of the aeroplane tests, as part of the machinery of the Golden Butterfly was controlled by foot pressure.

A council of war was in progress on the porch of the Prescott home.  The participants were the inseparable four.  Peggy and Roy, the latter with his injured foot on a stool, and Jess and Jimsy.  They had been discussing the case against Mortlake and Fanning Harding.  All agreed that things looked as black against them as could be, but—­where was the proof?  There was not an iota of evidence against them that would hold water an instant before impartial judges.