"Something ... something here," she said, "in this leucocyte. It's not a normal structure, but it's familiar. I've seen something like it before, but I just can't remember." She turned away from the scope and unthinkingly pressed her gory knuckles to her forehead. "I know I've seen it before." Brion squinted into the deserted microscope and made out a dim shape in the center of the field. It stood out sharply when he focused--the white, jellyfish shape of a single-celled leucocyte. To his untrained eye there was nothing unusual about it. He couldn't know what was strange--when he had no idea of what was normal. [Illustration] "Do you see those spherical green shapes grouped together?" Lea asked. Before Brion could answer she gasped "I remember now!" Her fatigue was forgotten in her excitement. "_Icerya purchasi_ that was the name, something like that. It's a coccid, a little scale insect. It had those same shapes collected together within its individual cells." "What do they mean? What is the connection with Dis?" "I don't know," she said, "it's just that they look so similar. And I never saw anything like this in a human cell before. In the coccids, the green particles grow into a kind of yeast that lives within the insect. Not a parasite, but a real symbiote--" Her eyes opened wide as she caught the significance of her own words. A symbiote--and Dis was the world where symbiosis and parasitism had become more advanced and complex than on any other planet. Lea's thoughts spun around this fact and chewed at the fringes of the logic. Brion could sense her concentration and absorption. He did nothing to break the mood. Her hands were clenched into fists, her eyes staring unseeingly at the wall as her mind raced. * * * * * Brion and Ulv sat quietly, watching her, waiting for her conclusions. The pieces were falling into shape at last. Lea opened her clenched fists and smoothed them on her sodden skirt. She blinked and turned until she saw Brion. "Is there a tool box here?" she asked. Her words were so unexpected that it took Brion a moment to answer. Before he could say anything she spoke again. "No hand tools, it would take too long. Could you find anything like a power saw--that would be ideal?" She turned back to the microscope, so he didn't have any opportunity to question her. Ulv was still looking at the body of the magter and had understood nothing of what they had said. Brion went out into the loading bay. There was nothing he could use on the ground floor, so he took the stairs to the floor above. A corridor here passed by a number of rooms. All of the doors were locked, including one with the hopeful sign TOOL ROOM on it. He battered at the metal door with his shoulder without budging it. As he stopped to look for a way in he glanced at his watch. Two o'clock! In ten hours the bombs would fall on Dis.