ng wide the rear doors of the garage. The
truck drove in, but not before Penny had riveted her eyes upon the
license number.

At sight of the last three figures, her heart leaped. The
numbers--684--were identical with those she had noted upon the license
of the service car at the Big Dipper!

CHAPTER XVII

Under the Canvas

"It begins to look as if my hunch might be correct," Penny told
herself. "Unless that truck merely drove into the garage for gasoline
or service, things look suspicious!"

She saw Brunner follow the car into the building, carefully closing the
doors.

"If everything is honest and above board, why did they use the alley
entrance when the other one is far more convenient?" she reflected.
"Obviously, Brunner knew the car was coming at exactly ten o'clock too."

Convinced that she was on the verge of important discoveries, Penny
settled herself for a long wait. From her chair by the window she
could watch both the alley and the main entrance.

A half hour elapsed, then another. At length Penny's patience was
rewarded. The alley doors swung open and a heavy truck which was
covered over with a canvas top, emerged. The driver wore a cap and his
head was bent low. In the semi-darkness of the dimly lighted street
Penny could not catch even a glimpse of his face.

"I must follow that truck!" she thought tensely. "If Dad were here he
would do it I feel sure! It's the only chance to gain real evidence!"

She waited at the window only long enough to see that the car had
turned down Center Avenue. Scribbling a brief message to her father
explaining what she intended to do, she left the note where he would
find it in the event he returned to the office that night. Then she
raced to the street.

By the time she had her roadster started the covered truck had
disappeared. However, turning down Center Avenue, Penny caught it at
the first traffic light. Satisfied that she would have no trouble in
keeping it in view, she slowed down, falling back to a distance which
was not likely to arouse suspicion.

Penny had no idea where the chase would lead, although the truck seemed
to be driving directly out of the city. From the slow rate of speed at
which it traveled, she thought that it must be heavily loaded with
cargo.

"If I only knew what was hidden under that canvas cover I might have
the solution to the mystery," she reflected. "I think I have it
anyway, but I must secure definite