The machine throbbed. He'd worked in the 'ponics room as a bio-tech, and he'd always taken the huge machine and its humming noise for granted. It was there, and that meant it had a purpose. It functioned; all you had to do was put oil into the little hole whenever the sound rose to a shriek. But now the purpose meant something. This generator kept the tanks going, producing air, food, water.... Ker-jon wielded his screw-driver clumsily. Only menials--formerly mutants and now non-mutants--played with such tools. If the Ark passed through a particularly brilliant area of space, if the blackness outside the ports in the astro-room churned into a seething mass of light, the menials used these screw drivers and fastened thin metal shields over the ports. _Insert it there, yes! And twist. See, the little plug comes loose. And now another._ Suddenly, the entire casing fell away, and Ker-jon peered into a maze of intricate wiring. _Remove that one, that one, and that one. Careful, don't touch that or you'll receive a shock--whatever a shock was_-- Without warning, the machine stopped its humming. Nearby, the liquid which bubbled away merrily in its vat gurgled once or twice, then subsided. The silence closed in from all sides. * * * * * Three days later, Ker-jon received a summons from Flam-harol. The ridge-head look worried, and he did not try to hide it. "You were a bio-tech first class, hydroponics division. I--I have a job for you." "Yes? What's that?" "Something happened. I don't know what, but a machine which used to hum doesn't do it any longer, and the vegetation in 'ponics looks a little sick. The level in the water-storage units is lowering--" Ker-jon wondered how long the air would last. He almost sensed a difference, a thickness, a necessity to breathe more deeply, perhaps more rapidly. His imagination, probably, because according to the books, air would continue to be manufactured as long as the plants lasted. "What do you want me to do?" Ker-jon said. "Fix it, that's what." "I can't." "What do you mean, you can't? Don't cross me, Ker-jon; I'll have you detained--" "That isn't what I mean. I know the humming machine you're talking about. I don't know how it works; no one does. Of course, we can find out. If we study the old records--" "Bah! Say, do you know any good astro-techs? The machinery in the astro-room doesn't work. I don't know the function of that room, Ker-jon, but I've heard it's important." "We've all heard that, but no one knows why. We could find out, though." "How?" "By studying the old books." Ker-jon wondered if it had been Ab'nath or the old albino who had tampered with the astro-mechanisms.