Free Out on Blue Six by Ian McDonald

sound.
    Unidentifiable in the sinister acoustic darklands of Shaft Twelve. Just: a sound. A presence.
    Courtney Hall took grip of the impacter and slid the output control up into the red. She had never used the tool even as a tool, much less a weapon, but the principle seemed simple. Point. Squeeze. What you pointed at exploded. From the hatchway she could survey all of Shaft Twelve. She held the impacter emission head against her chin, watching, listening. Water dripped from a pipe joint and fell, sparkling in the wan maintenance lights, down the center of the shaft to gather in a deep pool at the bottom.
    “Hello?” Courtney Hall ventured. “Helloooo.”
    Drip, plink. Drip, plink, drip.
    She aimed and fired with a unity of thought and action that dazzled her. There was a howl of power, an explosion, and all the lights went out. Shorted power conduits snaked and hissed and shed blue sparks toward the oil-dark lake. “Damn.” With one shot she had disabled the power and air systems for New Paris Community Mall. Within the hour Shaft Twelve would be a-buzz with environmental maintenance workers, crawling into, round, over, through every catwalk, access tunnel, gantry, hatchway, vent. They could not possibly overlook Courtney Hall’s fur-lined nest in the air-conditioning subsystems control room. “Damn damn damn damn.” But she had seen something. She was certain. A something—a someone? A what—a who? Light-starved, spindly, a pale shadow. At least that was one question answered. Contact with the others: unarguably undesirable.
    Surprising how few souvenirs of her furry little home she chose to take with her in her nightsac. A hammock, a bicycle lamp, a sleepsac, some cleanup tissues, a box of tampons (removed from the Compassionate Society’s regulation of her womanhood, she could not be certain her periods would not restart), a rope, a packed lunch, a bottle of mineral water (nongaseous), some clean underwear, some spare clothes, and shoes. The rest she left: stolen goods are worth exactly what you pay for them. But she did say good-bye to the hundred and seventy-four Wee Wendy Waifs. None of them seemed sad to see her go.
    Her early timid surveys of the warrenways about Shaft Twelve had disclosed no other potential living spaces. She must quit New Paris entirely and move into unexplored territory. Unexplored, potentially occupied.
    She tried not to advertise her presence too widely with the bicycle lamp. As her journey led her away from the upper levels, down into older, more chaotic strata of jumbled architectures, she left behind the artificial illumination to enter a stoop-shouldered country of brick tunnels, trickling water, and stygian darkness. Fear of the dark overcame fear of discovery. She fixed the bicycle lamp to her nightsac shoulder straps with a roll of electrical tape filched some days previously from another careless engineer. And she kept the impacter at the ready. Her swinging beam illuminated damp brick arches and fan-vaulted ceilings, brass pipes and corroded wheels of a curiously archaic design. A sense of having wandered far from Yu overcame her, in time as well as in space, of having left the city that was the world to enter an altogether other world coexistent with the Compassionate Society but secretive, inaccessible, an old world of damp, dark, and drippings that had survived, preserved unchanged by the darkness, since the time of the Break. She had come too far, too deep; she could feel history pressing on her stooped shoulders as she squeezed along the narrow brick intestines. She splashed ankle-deep through ancient fossilized rainwater and at every junction, every confluence of brick pipes, chose the upward path. But a claustrophobic awareness told her that the tunnels were redefining themselves before her, twisting and turning so that for every upward she chose, the tunnels moved to draw her down.
    There was no question of ever being able to find her way back to Shaft Twelve. It was