What interested him more was a door which he had not dared to hope he would find. It was bolted on his side, and when he had slid this back he discovered to his relief that it was not locked. He opened it carefully, first extinguishing his light. Beyond the door was darkness and he snapped back the light again. The room led to another, likewise empty. There were a number of shelves, a few old wine-bins, a score of empty bottles, but nothing else. At the far corner was yet another door, also bolted on the inside. Evidently van Heerden did not intend this part of the vault to be used. He looked at the lock and found it was broken. He must be approaching the main workroom in this new factory, and it was necessary to proceed with caution. He took out his revolver, spun the cylinder and thrust it under his waistcoat, the butt ready to his hand. The drawing of the bolts was a long business. He could not afford to risk detection at this hour, and could only move them by a fraction of an inch at a time. Presently his work was done and he pulled the door cautiously. Instantly there appeared between door and jamb a bright green line of light. He dare not move it any farther, for he heard now the shuffle of feet, and occasionally the sound of hollow voices, muffled and indistinguishable. In that light the opening of the door would be seen, perhaps by a dozen pair of eyes. For all he knew every man in that room might be facing his way. He had expected to hear the noise of machinery, but beyond the strangled voices, occasionally the click of glass against glass and the shuff-shuff-shuff of slippered feet crossing the floor, he heard nothing. He pulled the door another quarter of an inch and glued his eye to the crack. At this angle he could only see one of the walls of the big vault and the end of a long vapour-lamp which stood in one of the cornices and which supplied the ghastly light. But presently he saw something which filled him with hope. Against the wall was a high shadow which even the overhead lamp did not wholly neutralize. It was an irregular shadow such as a stack of boxes might make, and it occurred to him that perhaps beyond his range of vision there was a barricade of empty cases which hid the door from the rest of the room.