"Maybe you're right," Cron muttered. "I had a disagreeable hour with
that simple minded Mrs. Dillon. She's still afraid to notify the
police, but that Nichols girl has been talking with her, and she may
make us trouble."

"Christopher Nichols has been assigned to the jewel case too," Hoges
added. "He's no sloth when it comes to action!"

"Our game has just about played out," Cron agreed. "But I have one
more good customer lined up. I told him to come here at one-thirty to
see the picture."

"Maybe we could pull this last job," Hoges agreed. "Does he know much
about painting?"

"Very little. We ought to nip him for three thousand at least."

Hoges glanced at his watch.

"If your customer is coming at one-thirty we'd better get the stage
set."

"All right," Cron nodded. "Let's clean up the joint."

Uncovering the genuine Rembrandt, he took one of the copies, and deftly
inserted it in the picture frame behind the original painting, but in
such a manner that only the back of the canvas was visible. When the
frame was replaced only a person with keen eyesight could detect the
trickery.

"We'll pull the usual gag about identifying the picture with a
signature or a symbol," Cron muttered. "That always goes big."

By this time Penny had seen enough to understand how Mrs. Dillon and
other gullible customers had been duped. They had been shown the
original stolen Rembrandt, but when invited to place an identifying
mark on the back of the canvas to insure that they received the same
picture, actually signed the fake copy. It was then a simple matter to
remove the two paintings from the frame and send the customer the
worthless one which bore his mark.

"Cron and his confederates have worked a fairly safe racket too," Penny
thought. "Even if a customer learns he has been cheated, he's afraid
to go to the police for fear he'll expose himself as a person willing
to buy stolen property!"

She was not greatly surprised to learn that Cron was a party to the
dishonest scheme, notwithstanding that Mrs. Dillon had denied the art
critic was the mysterious agent who had visited her. Now Penny knew
that the woman had not spoken the truth. Doubtlessly, she had feared
to accuse Cron, lest he in turn expose her to the police.

A knock sounded on the door. Cron and his confederates froze into
tense attitudes, then relaxed.

"It must be our customer," Cron whispered. "Open the door."

As it swung back, Max