Penny jotted down the
number.

"Why did you want it?" Susan asked curiously. "You don't think that
man was trying to steal a wheel?"

"I certainly do. Otherwise why would he have left so hurriedly when we
came up? See, the wheel is only half changed."

They walked over to the nearby automobile to look. The wheel obviously
was a new one and apparently had not been damaged.

"That man was a tire thief all right," Penny announced. "It means that
the Molberg gang is starting activities again. I must get in touch
with Father immediately."

"I'll take you straight home," Susan offered.

"If I'd been just a little quicker I'd have caught the entire license
number," Penny said regretfully. "Even so, it may be possible to trace
the car."

Returning to their own automobile, they drove rapidly toward the
Nichols home.

CHAPTER XV

Incriminating Evidence

Penny found her father occupied at his desk in the study. Recounting
her experience at the Big Dipper, she offered him the license number
which she had copied.

"I don't suppose it will be of any use to you since I failed to get the
entire number."

"I may be able to trace the car though I rather doubt it," Mr. Nichols
told her. "At any rate, from what you've seen tonight I feel confident
that Rap Molberg is shipping another truck load of stolen wheels out of
town. I'll tip off the police to be on the lookout."

Some months previously the detective had installed a private wire which
connected him directly with the police station. He used it now to talk
confidentially with the police commissioner.

"I must go downtown at once," he informed Penny regretfully after
making the call. "Don't wait up for me. I probably won't return until
late."

At midnight Mr. Nichols had not come home. Penny, after dozing for
some hours in the big easy chair, went off to bed. Not until morning
at the breakfast table did she learn of the night's activities.

"As usual we failed to make a capture," the detective acknowledged
gloomily. "The police bottled up all the main highways leading from
the city. All suspicious trucks were searched. We thought certain
we'd catch Molberg with the goods, but he was just a little too smart
for us again."

"Were many wheels stolen last night?" Penny inquired curiously.

"A good truck load at least. This case has begun to make me look like
an amateur. If I don't begin to close in on the Molberg gang soon I'll
be the lau