of trickery
which would appeal to Rap Molberg. You say the door is operated by
means of a photo-electric cell?"

"That's what I think. At least when the beam of my light struck a
certain spot on the wall, the door opened."

Mr. Nichols arose and paced rapidly back and forth across the floor.

"I'm going to take you into my confidence, Penny," he said quietly.
"For days my men have been circling in on Rap and his gang. We've
located one of their hideouts, and we're raiding the place tomorrow
night. It now seems advisable to surround the Hamilton building
simultaneously. Then there will be no chance that any of the crooks
can use the underground ramp to make a get-away."

"Will the police make the raid?" Penny inquired curiously.

"Yes and no. So far I have taken only one man into my confidence."

"And who is that?"

"Jerome Davis."

"I was at his house this evening," Penny announced. "A threatening
note was thrown through the window while I was there."

She repeated the contents of the message.

"No doubt it came from the Molberg gang," her father said. "They are
doing everything in their power to intimidate Jerome Davis. But I
believe he is a man who can be trusted. Tomorrow night at eleven
o'clock he will be ready with a picked group of policemen. No one but
himself will know any of the details of the raid until it is actually
on. In that way there will be almost no danger of the information
leaking out."

"Where is this other hideout which is to be raided?"

"I can't tell you that. It isn't that I don't trust you, but sometimes
an unguarded word will destroy the work of weeks."

"I guess it's just as well I don't know too much about it ahead of
time," Penny agreed.

The conversation was checked as Mrs. Gallup came from the kitchen with
a tray of sandwiches and a tall pitcher of fruit juice. For a time
Penny and her father confined their talk to less vital subjects. But
when the housekeeper had gone from the room again, Mr. Nichols took up
the matter where it had been dropped.

"If my raids tomorrow night are successful, it will end the case. We
may need you, Penny, to show the officers how to get into the Hamilton
building."

"I'd like to help," she assured him eagerly.

"Good," Mr. Nichols said warmly as he picked up the evening paper.
"Until the appointed hour, don't go near the Plant. And mind, not a
word of this to anyone."

CHAPTER XIII

The Raid

At exactly ten