They pressed close against the willow tree and lowered their heads so that their faces would not be seen. Both were wearing dark clothes and dark caps. They did not look up, for they knew that their faces would be grey against the surrounding darkness and that Markel might see them. In an agony of suspense they heard the footsteps come closer. Markel poked around among the rubbish at the side of the mill. It was plain that he was not yet convinced that he had been suffering from a delusion when he saw the moving forms on the hillside and he meant to satisfy himself beyond any shadow of doubt that there was no one lurking in the vicinity of the mill. Nearer and nearer he came. His body brushed against the overhanging branches of the willow. He was now only a few yards away from the Hardy boys. Breathlessly, they waited. They stood, rigid and motionless, not daring to look up. Markel's footsteps came to a stop. He was standing but a short distance away, listening intently. Had he seen them? CHAPTER XXII THROUGH THE ROOF The Hardy boys always said that the few seconds in which they stood in the shadow of the willow tree with the suspicious Markel almost within arm's length of them, not knowing whether they had been discovered or not, were the longest seconds they had ever known. It seemed hours before they finally heard Markel give a grunt of satisfaction and trudge away in the opposite direction. Even then it was minutes before they dared move, before they ventured to raise their heads and look about them. When at last they did so, Markel was no longer in sight. They heard him go around the other side of the mill and finally they heard his footsteps as he trudged up into the doorway. The door banged at last. Markel was back in the mill. They breathed freely. "That was a close call," whispered Joe, in relief. "Not a sound," cautioned Frank. "They may be listening." They waited in the shadows for a long time. But evidently Markel had given up the search, his suspicions allayed. Finally a strange sound came from the interior of the mill, a strange whirring sound, followed by the muffled rumble of machinery. "What's that?" whispered Joe. They listened. The rumbling sound rose and fell with monotonous regularity. Finally Frank nudged his brother and pointed to one of the boarded windows half way up the side of the mill. A faint streak of light was apparent through a crack in the boards. "That must be where their workroom is," Frank whispered. The sound of machinery in motion continued. "We've struck them at the right time," said Joe, in a low voice. "They must do their work at night." "We've got to make sure." "How can we get inside the mill?" "The willow tree. We'll have to climb it and drop down on the roof." "What if they hear us? We won't have a chance to get away."