ust such
trickery."

"How?"

"When I viewed the picture and satisfied myself as to its quality, I
marked the back of the canvas with a tiny symbol. In that way you see,
another painting could not be substituted, for the marking would be
absent."

"The symbol might be duplicated."

"No, I would instantly detect the difference."

Penny sat lost in thought for a moment. She now understood the
significance of the strange marking on the back of the Rembrandt which
had puzzled Amy and herself. Was it possible that the Coulter girl had
been mistaken in the quality of the painting?

"Mrs. Dillon," she said after a long silence, "you confidently believe
that your painting is the same one which was stolen from the Gage
Galleries?"

"All I know is that my picture is a genuine Rembrandt. I did not learn
that a picture had been stolen from the museum until after I had made
my purchase. I do not know even now that I have this same painting."

"In the event that it is the same, you wish to return it to the museum?"

Mrs. Dillon glared at Penny in frank dislike. She had been fairly
trapped and knew it.

"Of course," she replied coldly. "I hope you do not think I would
intentionally keep stolen property?"

"I thought you would see it that way," Penny declared, smiling. "And
with your cooperation, the police should be able to capture the real
culprits."

"What do you want me to do?"

"When will you see this agent with whom you dealt?"

"He is coming either today or tomorrow for the second payment."

"I don't need to advise you to refuse to give him any more money. But
I wish you would try to learn from him the names of the original
dealers who handled the picture."

"I'll try to find out."

"And another thing, Mrs. Dillon. You must notify the Gage Galleries
immediately that you have the Rembrandt."

The woman made no response.

"You will do that?" Penny asked.

"Yes," Mrs. Dillon answered harshly.

"I'll see you again tomorrow," Penny said, arising to depart. "Until
then you have my promise that I will not talk with the police."

"I have nothing to fear from them," Mrs. Dillon announced proudly.

"Not if you show a willingness to cooperate," Penny agreed. "When you
think the matter over, I believe you will decide to reveal the name of
your friend--the agent who negotiated the sale."

She waited an instant, hoping that Mrs. Dillon would reconsider. When
the woman did not speak, she turned and