Penny Nichols and the Black Imp - Joan Clark

"It occurred to me, Mrs. Dillon, that possibly you could help in locating the stolen picture."

"I? You flatter me, my dear."

Penny saw the warning in Mrs. Dillon's dark eyes. But she dared to go on.

"Let's not pretend, Mrs. Dillon," she said quietly. "I know about that painting which you keep hidden behind the panel of the library."

Mrs. Dillon sprang to her feet, her face convulsed with anger.

"So you are the snooper who came here!" she cried. "Get out of my house and never, never come again! Go quickly or I'll call the police!"

Penny listened calmly to the woman's tirade, making no move to obey the impolite command.