"It will be wise to go in a taxi, I think," she remarked. "There should be less danger of anyone recognizing you that way."

While Amy changed her clothes, Penny went downstairs to call a cab. It came twenty minutes later and the two drove directly to Mrs. Dillon's residence.

"The coast should be clear," Penny remarked as they alighted at the door. "It's a quarter to one but Mrs. Dillon surely is on her way to meet Cron by this time."

Penny boldly rang the doorbell. Presently a maid answered the summons.

Smiling graciously, the girls stepped inside without waiting for an invitation to do so.

"Tell Mrs. Dillon, please, that we have come to see the picture," Penny directed confidently.

"Mrs. Dillon isn't in, Miss."

"Not in?" Penny exclaimed, and turned to Amy in pretended chagrin. "Do you suppose she forgot our appointment?"

"I am afraid so," Amy murmured.

"Mrs. Dillon went away in a great hurry," the maid said apologetically.

"She didn't mention that she was expecting guests."

"She failed to say that she invited us here to view the painting?"

"It was an oversight, of course. Mrs. Dillon will be sorry I know to have missed you. Your names--"

"It will be some time before we can come back I fear," Penny interrupted quickly. "And we did so want to see the picture. I don't suppose you could show it to us?"

"I am afraid not. I don't even know what picture she meant."

"Oh, the one hanging in the library," Penny informed. "It would only take us a minute to look at it."

"Why, I guess I could show you that picture."

Forgetting that she had neglected to learn the names of the callers, the maid led them to the library. The girls pretended to study the ugly painting which hung over the mantel.

"Is this Mrs. Dillon's last purchase?" Penny inquired.

"It's the only picture she's bought recently."

The girls shrewdly concluded that the maid was unaware of the hidden panel and were at a loss to know how they could manage to view the Rembrandt.

"I could study a beautiful painting for hours and hours," Amy remarked, sinking down into a chair opposite the mantel.

"So could I," Penny agreed, gazing with a rapt expression at the hideous picture. As an apparent afterthought she turned to the maid who stood waiting. "If you don't mind, we'll just sit here for a few minutes and admire it."

"Certainly, Miss. If you'll excuse me I'll go on with my dusting."

The instant the maid had gone from the library, Penny pulled on the silken rope and the hidden panel was revealed. She jerked aside the velvet curtain to disclose the Rembrandt.

"You'll have to make a quick examination," she warned. "That maid may come back any minute."

Amy studied the painting critically. When she did not speak, Penny impatiently asked for her opinion.

"I believe it's merely a copy of the original, although a rather clever copy. Rembrandt was very skillful in his method of handling light and shade--in this picture it is all lost."

"Then I was right!" Penny cried triumphantly.

"My opinion may not be right, Penny. If I could see the painting in a better light--"

With an anxious glance toward the library door, Penny hastened to the window and pulled aside the heavy draperies. A beam of sunlight fell across the picture.

"Yes, I'm sure it's a fake," Amy decided firmly. "If Mrs. Dillon bought this for the original Rembrandt she was cheated."

"Well, she deserved to be. She shouldn't have tried to buy stolen property."

"Let me look on the underside of the canvas," Amy suggested.

"Sometimes that will give a clue as to the age of a painting."

They pulled the picture out from the wall and peered behind it.

Directly in the center of the canvas was a strange, complicated symbol and beneath it the initials, "G. D." Both had been inscribed in India ink.

"What's that for?" Penny questioned.

"I wonder myself," Amy replied.

"Then it isn't customary to put symbols or initials on the back of a painting?"

"Decidedly not."

The girls studied the marking for a minute. They could make nothing of it.

"I can't explain the symbol," Amy said, "but I'm convinced this painting is a fraud."

Penny had expected such a verdict as it confirmed her own observations, but for her friend's sake she was sorry that the painting had not turned out to be the original Rembrandt. Had they actually located the stolen picture it would be a simple matter to lay their evidence before the police and demand that Mrs. Dillon be forced to reveal the dealer from whom she purchased the property.

"Everything is in a queer muddle now," Penny commented thoughtfully.

"Mrs. Dillon really isn't guilty of any crime at all, for she didn't buy a stolen picture. We can't very well cause her arrest."

"Mrs. Dillon should complain to the police that she was cheated."

"She doesn't know it yet," Penny chuckled. "When she finds out about it, I imagine she'll never report the dealer. Her own part in the affair would be too humiliating. Even if she didn't buy stolen property, that was her intention."

"I suppose the real crooks counted upon just such a reaction," Amy said. "When they sold her that fake painting they knew they were safe."

"And in the meantime the genuine Rembrandt is still missing," Penny replied musingly. "I have a suspicion this dishonest dealer, who sold Mrs. Dillon the fake picture, might be able to throw a little light upon the subject."

"But how will we ever trace him unless we notify the police?"

"I am afraid that would be a sure way of losing his trail completely,"

Penny replied. "Mrs. Dillon's arrest would be the signal for the dishonest dealer to get out of town."