“Not a word!” was the reply. “But we’ll try with the library door open! I’ll go back to the hall and you start again!” A thoughtful look on his face, Robin turned quickly and, hurrying round the side of the house, entered by the front door. Standing by the door leading to the library corridor he found Manderton. The detective did not seem particularly glad to see him. “Good-morning, Inspector,” said Robin affably, “you’re early to work, I see. Having a little experiment, eh?” Manderton nodded without replying. Then the stentorian tones of Sergeant Harris proclaiming the views of “The Thunderer” on the Silesian situation rolled down the corridor and struck distinctly on the ears of the listeners in the hall. Presently Manderton closed the corridor door, shutting off the sound abruptly. “I think you said you could not hear the sergeant with the library door shut?” queried Robin suavely. “With the door shut—no,” answered the detective shortly. “But with the door open ...” He broke off significantly and dropped his eyes to his boots. “Would it be troubling you,” Robin struck in, “if we pushed your experiment one step farther?” Manderton lifted his eyes and looked at the young man, Robin met his gaze unflinchingly. “Well?” There was no invitation in his voice, but Robin affected to disregard the other’s coldness. “Let the library door be shut,” said Robin, “but leave the glass door leading into the garden open. Then give Sergeant Harris another trial at his reading....” The detective smiled rather condescendingly. “With the library door shut, you’ll hear nothing,” he remarked. “The library window is open,” Robin retorted, “or rather it is as good as open, as one of the two big panes is smashed....” His voice vibrated with eagerness. The detective looked at him curiously. “Oh, try if you like,” he said carelessly. Without waiting for his assent, Robin had already plucked open the corridor door and was halfway down the passage as the other replied. He was back again almost at once and, motioning the detective to silence, took his place at his side by the open door. Then the sound of the policeman’s voice was heard from the corridor. It was muffled and indistinct so that the sense of his words could not be made out. But the voice was audible enough. Robin turned to the detective. “Bude could make out no words,” he said. “But how do we know that the glass door was open?” queried the detective sceptically. “Because I left it open myself,” Robin countered promptly, “when I went out for my walk before tea. Sir Horace told me that he found the door banging about in the wind when he went out to get into the library by the window.” Mr. Manderton allowed his fat, serious face to expand very slowly into a broad, superior smile.