What Is the Motive of the Extortion of a Persian Prince?

According to Dorothy's sister, dorothy did not believe that frank knew anything about the prince. He seemed genuinely pretty shocked when the police presented him with the letters and the fact that she had saved six thousand dollars and he didn't know it. That tells me whell she wasn't planning on staying with him. She's planning on taking that money and going to one of her suitors. And it sounds like its gong o be the prince.