l. It is very important."

"Just a minute please."

There was another long wait, then the telephone operator informed Penny
that the call could not be traced. It had been made from a pay station.

Mr. Nichols entered the office just as Penny hung up the phone.

"Anything wrong?" he asked quickly, noticing the expression on her face.

Penny repeated the warning message.

"Well, it looks as if I'm on the right trail," Mr. Nichols declared,
not in the least disturbed. "I'd have preferred that the Molberg gang
hadn't learned I was shadowing them, but such news travels fast through
underground channels."

"I'm afraid some of those dreadful men may harm you," Penny said
anxiously. "Promise me you'll be careful."

"I am always careful, my dear, but I refuse to go around wearing a
bullet proof vest. This isn't the first warning telephone call I've
received."

"I suppose not," Penny sighed. "But I should think that if the members
of the Molberg gang know you have been assigned to the case, it would
be hard to secure evidence against them."

"It won't be easy," the detective agreed. "However, I flatter myself
that I have a few trained investigators whose activities will never be
suspected."

"You mean they mingle with underworld characters and try to gain their
confidence?"

"Yes, that's the usual plan. When I locate Rap Molberg I'll have him
constantly shadowed."

"I've never seen many of your assistants around the office," Penny
remarked.

"Naturally not," Mr. Nichols smiled. "If they came here to report,
every crook in Belton City would be aware of it within an hour."

"Then how do you keep in touch with your men?" Penny asked curiously.

"There are a few secrets which I must keep to myself. Aren't you
taking a rather sudden interest in my work, Penny?"

"Perhaps I am. Since my car wheels were stolen I feel personally
concerned in the case. I wish I could do something to help."

Mr. Nichols became grave. "There is nothing you can do, Penny. The
last thing in the world that I could wish would be to have you involved
in the case. In fact I've been worried for fear----"

"For fear of what?" Penny demanded as her father checked himself.

"I've been afraid that the Molberg gang might attempt to strike at me
through you. Until this case is finished you must be very careful."

"I'll be careful, although even for you I refuse to go around wearing a
bullet proof vest," Penny grinned, paraphrasi