But the rear portion of the house was without windows or doors. It was not too apparent from the outside, but Birkala had been in Erik's house many times and had discovered long ago that there was a large section of it closed and inaccessible. As fast as his short legs could move, Direka led Birkala through the simply furnished house. Birkala followed easily, and smiled. Direka was like a monkey; he was not bright, but he was clever and eager. In Erik's bedroom, Direka stopped, panting, and pointed triumphantly at the rear wall. There was a great crack in it, near Erik's bed. A section of the wall was a secret door, and it had been left ajar. "Good fortune!" breathed Birkala, his eyes sparkling. "I have wondered for a long time what was behind that wall." He pushed the door wider and went through the opening, Direka crowding at his heels. It was very dark, the only light coming through the crack from the bedroom. Birkala could see nothing. He felt about the walls for a switch, without success. "I wonder how one turns on the light in here?" he said to Direka. At the word "light", light sprang into being all around them. It was a soft, indirect illumination which appeared to have no source and cast no shadow. They were in a sort of corridor which paralleled the wall through which they had just come. On the opposite wall of this hallway were banks of dials and charts and switches, and in the center of this opposite wall was an open doorway. Cautiously, Birkala and Direka moved down the corridor and peered through the open door. It gave entrance to a square room, which was lighted with the same sort of illumination as the hall. There was nothing in the room. There were just four walls, a ceiling and a floor. There was no furniture. There were no windows and there was no other door. "A strange thing!" muttered Birkala. "Erik does not retire to this place, for he is always around the house. I have walked into his bedroom and found him asleep. What is the purpose of this room?" "Perhaps a dungeon," darkly suggested Direka, who was a devotee of adventure pictures at the theaters. Birkala backed away from the door and studied the array of dials and switches. As Erik had said, Birkala was a good scientist. Birkala was thoroughly familiar with the nervous and intestinal workings of spaceships. He had made several trips to other planets in Orcti's system, and had made several contributions of his own to the science of rocketry and astrogation. He whistled softly between his teeth. "We've found it, Direka!" he exclaimed to his companion. "This is the beam transmitter that Erik has kept hidden so carefully. This is the control panel, and the room undoubtedly is the transmitter itself." Direka looked puzzled, then brightened. "Now we can go to Earth? Yes, Birkala?" he chirped. * * * * *