have been locked up for hours. If the leader of the Silver Masks was
among them he'd have taken charge hours ago."

"Unless," Blake said thoughtfully, "he didn't want any of us to _know_
he was the leader."

O'Toole pulled the mask down over his eyes.

"Let's get out of here," he said. "You've got something up your sleeve
and I'll play the cards the way you want them."

"One more thing," Blake told him. "These men had to have a track to get
Mono 6 into this cave. When it goes out again we'll be on the same
track, but it will end in a canyon or deep lake."

"Go on."

"Well! We've got to get started on that trip. After we are out you and I
will have to take our chances of stopping the mono."

"And I thought Grudge Harror was a tough baby," O'Toole grinned.

* * * * *

"It isn't a matter of being tough," Blake said. "Can you handle the
engine room alone?"

"Handled it for years," O'Toole said coolly. "But I'd like to know where
that track ends."

"You will." Blake went toward the door. He gripped O'Toole's shoulder.
"You're a good Irishman, O'Toole. Now go out of here and straight to the
cab. I don't think they'll dare send one of the other men. If the
controls are tied into place, leave them alone. When I signal, set all
motors going full speed. Sit tight and keep her flying."

"And the end of the track?" O'Toole asked. "If I don't get shot in the
back before I'm half way across the cave, how do I know when to stop?"

Blake chuckled dryly.

"Perhaps you won't," he admitted. "But I'll be in the rear lounge with
every male passenger within my sight. One of them is bound to break down
when he knows he's at the end of the trail."

"So?"

"I'll jerk the emergency cord," Blake said. "Set your brakes the minute
you hear it. O'Toole, it's a long chance but we've got to take it."

"One more thing," O'Toole asked. "Blake, who in hell is the leader of
the Silver Masks?"

Blake hesitated, his face darkening. He opened the door and pushed
O'Toole out gently.

"If I'm not mistaken," he whispered evenly, "Walter Ferrell knows more
about this than he's telling."

* * * * *

The gang of Silver Masks were gathered around the front end of Mono 6 as
Holly O'Toole and Jeff Blake emerged from Harror's office. They walked
swiftly toward the cab, and Slater who had evidently been waiting,
stepped from the crowd and came toward them.

"How about it?" He a