ith it!" shouted the old man, tremendously
excited. "Why, you can't, possibly! Philip Holmes'll track you
down--he'll tell the police--he'll rescue us! And then--"

Quade smiled suavely. "Oh, no, he won't. Perhaps you remember the shot
that sounded from the water-hole? Well, when I and my assistant, Juan,
heard Holmes say he was going for water, I told Juan to follow him to
the water-hole and bind him, to keep him from interfering till I got
back up. But Mr. Holmes is evidently of an impulsive disposition, and
must have caused trouble. Juan, too, is impulsive; he is a Mexican.
And he had a gun. I'm afraid he was forced to use it.... I am quite
sure Philip Holmes will not, as you say, track me down."

David Guinness looked at his daughter's white face and horror-filled
eyes and suddenly crumpled. Humbly, passionately, he begged Quade to
take her back up. "Why, she's never done anything to you, Quade!" he
pleaded. "You can't take her life like that! Please! Leave me, if you
must, but not her! You can't--"

* * * * *

But suddenly the old man noticed that Quade was not listening. His
head was tilted to one side as if he was straining to hear something
else. Guinness was held silent for a moment by the puzzled look on the
other's face and the strange way he was acting.

"Do you hear it?" Quade asked at last; and without waiting for an
answer, he knelt down and put his ear to the ground. When he rose his
face was savage, and he cursed under his breath.

"Why, it's a humming!" muttered Professor Guinness. "And it's getting
louder!"

"It sounds like another borer!" ventured Sue.

The humming grew in volume. Then, from the ceiling, a rock dropped.
They were looking at the cavern roof and saw it start, but they did
not hear it strike, for the ever-growing humming echoed loudly through
the cavern. They saw another rock fall; and another.

"For God's sake, what is it?" cried Guinness.

Quade looked at him and slowly drew out his automatic.

"Another earth-borer, I think," he answered. "And I rather expect it
contains your young friend Mr. Holmes. Yes--coming to rescue you."

For a moment Guinness and his daughter were too astounded to do
anything but gape. She finally exclaimed:

"But--but then Phil's alive?"

James Quade smiled. "Probably--for the moment. But don't let your
hopes rise too high. The borer he's in isn't strong enough to survive
a fifty-foot plunge." He was shouting no