"Very well. And now, another matter. This woman who brought the message to you is, you say, an agent of the police. Did she attempt to explain how she came by the message?"
"Yes. She was forcibly abducted, last night, carried a long distance out into the country, and the instructions given her. She was brought back to Paris, blindfolded, tonight."
"Mr. Stapleton, what would you say were I to tell you that less than an hour ago I saw this woman in the rooms of Alphonse Valentin, a man whom I suspect to be very deeply concerned in the kidnapping of your son?"
Stapleton started. "Is it possible?" he said. "Have you any idea what she was doing there?"
"No. They seemed on excellent terms, however. Of course, it is not impossible that an agent of the police might pose as a friend of one of the criminals, and thus obtain information. But it looks decidedly queer."
"It does, indeed. Still, as I said before, if I get my boy back, I shall be satisfied." He took a turn about the room, chewing nervously upon his long black cigar. "Now, Mr. Duvall, what is your plan to capture these fellows?"
Duvall sat in deep thought for sometime. "It is not an easy matter, Mr. Stapleton, but there is one way which promises success, and that, too, without interfering with your arrangements to recover your boy."
"What is it?"
"This. It is necessary for us, in some way, to identify the car which gives you the signal of the blue light. It will pass close to you, at a moderate speed. I want you to mark that car, so that it may be recognized at once."
"How can I do that?"