After a moment's thought, he began touching each tile within reach of the door. Most of them brought a response from Big Joe. He found four that did not. He knelt down before the door to peer at them closely. The first was unmarked. The second bore a dot in the center. The third bore two, and the fourth three--in order of their distance from the door. He stood up and stepped inside again, standing on the first tile. Big Joe remained motionless. He stepped diagonally left to the second--straight ahead to the third--then diagonally right to the fourth. He stood there for a moment, trembling and staring at the Sleeper. He was four feet past the door! Having assured himself that the monster was still asleep, he crouched to peer at the next tiles. He stared for a long time, but found no similar markings. Were the dots coincidence? He reached out with the pike, then drew it back. He was too close to the Sleeper to risk a mistake. He stood up and looked around carefully, noting each detail of the room--and of the floor in particular. He counted the rows and columns of tiles--twenty-four each way. Twenty-four--and there were twenty-four numbers in the series that was somehow connected with safe passage through the room. He frowned and muttered through the series to himself--0,1,2,3,3,3,2,2, 1.... The first four numbers--0,1,2,3. And the tiles--the first with no dots, the second with one, the third with two, the fourth with three. But the four tiles were not in a straight line, and there were no marked ones beyond the fourth. He backed out of the room and studied them from the end of the corridor again. Mara had come dizzily awake and was calling for him weakly. He replied reassuringly and turned to his task again. "First tile, then diagonally left, then straight, then diagonally right--" 0, 1, 2, 3, 3. A hunch came. He advanced as far as the second tile, then reached as far ahead as he could and touched the square diagonally right from the fourth one. Big Joe remained motionless but began to speak. His scalp bristled at the growling voice. "_If the intruder makes an error, Big Joe will kill._" Standing tense, ready to leap back to the corridor, he touched the square again. The motionless behemoth repeated the grim warning. Asir tried to reach the square diagonally right from the fifth, but could not without stepping up to the third. Taking a deep breath, he stepped up and extended the pike cautiously, keeping his eyes on Big Joe. The pike rapped the floor. "_If the intruder makes an error, Big Joe will kill._" But the huge figure remained in his place. * * * * *