Now he was fairly within the tunnel, which had been hollowed out of the earth, and lined with stones to prevent a cave-in. On Tom ran, calling from time to time, but he could no longer hear his companions’ voices. At first a fear came to him that he had been discovered, and his chums removed to some other part of the mill. Then he realized that, because of some peculiar acoustic property of the tunnel, he could only hear them at the heap of stones. On and on he ran. Presently he came to an old door that closed the tunnel. The portal was locked, but a few blows on the rotting wood from the hatchet opened the way for him. He saw before him a flight of stairs leading up, and opposite the lower landing was another door. “This is the secret staircase,” decided Tom, “and that other door is the way they get into it from the second floor of the mill, but it must be pretty well concealed. I’m in between the walls now, and the boys are up there!” He paused a moment to flash his light upward, and saw that the coast was clear. Then up the stairs he bounded. He listened as he reached the top, and heard the murmur of voices. “Here I am, boys!” he cried. “Tom! Tom!” came the answering shout. At the head of the stairs was another door. Tom pushed on it, but it resisted his efforts. “No time now to stop at trifles,” he murmured. “I’m going to smash it!” and smash it he did. It gave way with a crash, and Tom fairly tumbled into a large room. A hasty glance around showed that the apartment was empty, and another look disclosed the gun, fixed to the window sill in such a way that it looked as if someone was pointing it. “And that nearly fooled me!” mused Tom. “But where are the boys, I wonder?” He looked about. The room was a large one, and, opening from it were several apartments and halls. They were rudely fitted up, and in one were a stove and cooking utensils. “Here’s where the hermit has been living,” thought Tom, “and I guess the others have been hanging out here with him, too. But where are my chums?” There was no sign of them in any of the rooms, and for a moment our hero feared it had all been some dream--even the sound of the hidden voices. And yet he knew it could not be a dream. “Jack! Dick! Bert!” he called. “I’m here! Where are you?” He paused, listening for an answer. It came, faint and as though from afar off. “Here we are,” replied a voice. “We’re in some secret room. Listen while we pound on the wall, and that may guide you.” There came a faint tapping. Tom strained his ears to listen. He advanced toward one wall, and then to another, until he had located the place where the sound was heard most plainly. “I get you!” he cried. “The secret door must be somewhere around here. Here goes for a try at it.”