Manning silenced him with a gesture.
"I don't think I shall be very much in your debt by the time I have finished with you, Dryden," he replied pleasantly.
A queer exclamation from de Roda, who was crouching in front of the fireplace, broke in suddenly upon our conversation.
"You were right," he cried hoarsely, "you were right, doctor! It is here! I see it myself."
He pointed with trembling fingers towards a small ornamental knob in the centre of the grate, which I had noticed on several occasions bore a rough resemblance to a bull-dog's head.
Manning glanced round unconcernedly, and then turned back to me.
"You must excuse me for a moment," he said. "Mr. de Roda is naturally impatient."
He walked across to the hearth, and the gaunt, huddled figure of the other moved aside to make room for him.
"Now we shall see," he remarked. "It will be very disappointing if I am wrong after all."
He caught the knob in both hands, and, bending forwards, gave it a sharp wrench. Instantly, and without the least noise, the whole front of one of the side pillars swung open like a door, exposing a high narrow cavity lined with brick.