"Yes, that's all very well," replied Atherton. "But how do you account for the finding of the silver stuff in the underground chamber?" "Perhaps Tassh meant to hide it there, or it was too heavy for him to carry any farther," suggested Mayne, as he rested on the edge of a step his end of the staff from which the bowl was slung. As he did so the end of the pole touched the stonework at the side of the staircase. The slab of granite trembled visibly. "This part of the wall is quite loose," exclaimed Mayne. "Steady," whispered Atherton, warningly. "Keep quiet, you fellows." The Leader felt the face of the granite slab. It was certainly loose, but the joints of the masonry were not wide enough for his fingers to obtain a grip. "Hold my lantern a minute, Phillips," he said. "I'll see what I can do with my knife. You have matches handy? Good! Now blow out all the lights." These orders were promptly carried out. The darkness was darkness indeed. To the excited lads it seemed to have weight. Even Phillips, strong-minded as he was, grasped his box of matches tightly, as if he derived some consolation from the fact that he held a weapon that could be used to effectually banish the stifling sensation imparted by the intense darkness. Scratching lightly with the blade of his knife, Atherton at length found the joint of the stonework once more. Deftly inserting the blade, he cautiously prised the block of granite. It gave, then slid back in its position. "The stone is pivoted," he whispered. "Where's your hand, Mayne? Put it here, and when I swing the stone out half an inch try and get a grip." The blade bent almost to breaking point. The stone swung outwards. Mayne, gripping the rough edge, sought to retain a tenacious hold. "It's slipping," he gasped in low, tense tones. Atherton instantly drove the blade home till the handle was tightly wedged in the enlarged orifice. Then, relaxing his hold upon the knife, he aided Mayne with his wiry fingers. The block swung stiffly outwards another inch, then with hardly any resistance it turned, disclosing an aperture sufficiently large for a man to crawl through. The sudden rush of daylight blinded the lads, but at length their eyes grew accustomed to the scene. They found themselves looking into the room in Polkerwyck House that had been the rascally butler's quarters. It was not untenanted. Seated in a canvas deck-chair, with his back turned to the secret opening, was a man. Only the back portion of his head was visible above the top rail of the chair. "It's Tassh," said Atherton to himself. The question was how the Scouts were to act. To crawl through the narrow opening one by one and throw themselves upon the culprit was a business that was not only fraught with danger but well-nigh impossible to perform without giving the man due warning. Yet to Atherton it seemed the only way.