"I think the light would be red. He can make either, very simply, by means of a powerful electric searchlight—one of these pocket affairs, you know, fitted with colored glasses."
"You interest me wonderfully, Monsieur Duvall. What next?"
"It is, of course, most important that the signal given shall be the correct one. There must be no interference whatever with this fellow's escape—up to that point."
"Ah—I begin to see. And what after that?"
"First, let us continue with François. He will, I think, return a blue signal to the man in the automobile, to show that he has seen, and understood. He has the means to do so all ready, in his room."
"And then?"
"He will make, I think, a similar signal from his south window to some one who is on watch, in the direction of Passy. This second person, who no doubt has the child in his care, will then go to a telephone, transmit the address of the house where the child is hidden, to Mr. Stapleton, and quietly depart, to join his confederate in—say—Brussels. He will run not the slightest risk of capture. If, on the other hand, that message fails to go through, the address will not be telephoned, and the child will probably be killed."
Vernet frowned grimly. "It is a remarkable plan, Monsieur. These fellows are no bunglers. I think, however, that we shall be able to stop them."
"How?"
"I will station myself at the Porte Dauphine with a fast automobile, a racer. When these fellows pass, I will follow them, and overtake them."