"Say, whatever does all this mystery mean, Frank?" asked Bob, almost helplessly.
"Just what you might imagine; that there's danger hanging about us, Bob."
The eyes of the astonished Bob sought the ground at the point where his chum had been so deeply interested.
"Then it must be something you just discovered there, and that's a fact," he declared; "because you didn't act this way three minutes ago."
"I happened to discover footprints coming from another quarter," Frank went on, calmly; "and they headed into this crevice, just as those of the moccasined Moqui did from that side. And they came after old Havasupai had gone up, for I found where they wiped out a part of one of his tracks."
"Footprints, and were they made by the old professor, do you think?" asked Bob.
"Not any. Fact is," observed Frank, as though deciding to have the worst over, "they were the tracks of three persons, all men!"
"Oh! my! three, you said, Frank; and that would mean Eugene, Spanish Joe, and Abajo, wouldn't it?"
"Just the very ones I meant," replied Frank.