A (very short) short-story I wrote for a class in college, based off of an older idea I had. It's a "zombies-but-don't-say-zombies" thing that I would call "artfully vague" in terms of what the threat actually is.
 

Rebecca Curie lived in a world of minutes. To her, breathing was a sign of good fortune and every minute spent alive was something to be thankful for. To her, there were worse things than living life on the run.

This had been her brother’s route. Once a week, every Monday, leaving at dawn, he would go out into the world and bring back what the colony needed to last a little longer. And then one time, he simply did not return. Becca had taken over his job as Runner in hopes that she would find him holed up somewhere in the city.

That was a month ago.

“‘Rule #1,’” She said to herself as she stared at the path before her. “‘Do not take any unnecessary risks.’” She went through the checklist aloud every time. “Rule #2: Take no more than what will fit in the backpack. Rule #3: The gun is a last resort only.’” She took a deep breath. “‘Rule #4: If you get bit, don’t come back.’”

She took off before she could think of turning back. Up the fence, over onto the sidewalk, across the street and up the fire-escape before They even knew she was there. She had become good at being quick and quiet.

The apartment building had nothing in it, having been cleaned out by scavengers, refugees and Runners long before she ever started doing it; but two blocks further in was a store that she had been going through. Her feet pounded the well-tread path of the fire-escape. Whether or not They heard her was of little consequence, They could neither jump nor climb and very few wandered all the way to the rooftops.

Her supplies shook about in her pack: one day of food, one day of water, a knife, a gun, a crowbar, chalk and a flashlight. She had to pack light to make more room for supplies and to fight the notion of safety that having enough of anything brought. No one was ever safe and those who felt they were did not last long.

Becca came to the first jump. The two buildings were almost even in height and the gap was a narrow one caused by an alleyway below, but it still made her nervous. She put one foot up on the edge of the roof and glanced down. Dim shapes milled about in the shadows beneath her.

“Just don’t look down.” She said in a voice that offered little reassurance. Her right foot joined her left on the building’s rim and she jumped.

Landing always hurt a little, but hitting her shin on the edge of the roof was not the worst that could happen. Nothing to stop over, so it was across the roof, past the ducts of the air unit and over another gap and so on. Four buildings, then it was down a ladder into an alley to cross the street.

She clung to the ladder, some ten feet from the bottom, staring down. It looked clear, as clear as could be hoped for at least. The alley she was about to land in was dark and empty, except for an old dumpster that had not seen use in years. It was quiet, though, and she did not feel that it would pose any immediate danger.

Becca landed in a crouch, immediately backing against the wall. To her right, a low, resonant sound drifted in from the street; a hoarse exhalation, a dragging, thumping sound. It was coming closer. A wind blew through the alleyway, carrying with it a groan of unrest. One of Them was there, a few yards away, just on the sidewalk. The sound of its bare steps, the stale and ruined stench; Becca shut her eyes and held her breath. They could see only a little, but Their hearing was sharp and they could chase until Their muscles broke down and their bones gave out.

And that could take days.

The Thing kept going and it passed her by. She moved to stand up and found her hand aching, her knuckles were white against the grip of her crowbar. She let it go reluctantly and moved closer towards the street. The one that had passed was still walking away, but two were loitering in the street, milling about an old, rusted-out car. Two more were a little up the road.

Alright, Rebecca, you’ve done this before. Just out, around to the left of the car, then into the alley and up the fire escape. They won’t even notice you.

She was out in the street, her back bent forward and her hand on her weapon. Her feet moved her around the car in a wide circle, always facing towards the two shambling forms and watching for the slightest hint of energetic motion. She got her back against the front window of an old store and shifted her gaze from the street to the next alley and back. It was clear, so she snuck in and started climbing.

What had once been a store was now a hollowed out shell with little else than rotting food and broken shelves. Becca’s predecessors had been through it dozens of times, taking cans of food and bottles of medicine and leaving behind a sense of utter desolation.

She turned on her flashlight. It flickered dimly about the ruins of the second floor. The battery was supposed to recharge with movement, but it never seemed to work right. The rooms had once been used as offices and storage, but nothing was left in them now but graffiti scrawled by survivors long-since passed. Empty cans, lined with mold, lay rancidly about the place. The stairway down showed signs of having once been barricaded and, worse, dark red-brown blotches covered the walls and down onto the floor. It took time for people to realize that living in a city was no longer practical.

The ground-floor was a sea of refuse and scrap-metal. Security shutters covered the front windows and door and a variety of heavy objects had been placed against them. The result was darkness, but safety and security from the Things outside.

Becca’s first job was to find food. She had hoarded some cans and bags together, things that she had found but was unable to take back all at once. A large bag of dried corn and some freeze-dried apple slices, two cans of powdered milk and a package of salt, she fit these nicely into her bag with some room to spare. Her next goal was medicine; Mrs. Thomas was having migraines again and the colony was running low on antibiotics, these were problems that were hers to address.

Medicine was more difficult to than corn and salt, but Becca hoped to find at least something to help with the migraines. The medical section had suffered repeated ransacking over time and antibiotics would almost certainly not be amongst the scattered contents.

A pile of destroyed shopping carts sat inexplicably amongst the spilled contents of several old pill-bottles. This curious construction had been an object of Becca’s interest before, but there was no time to stop and investigate every little artifact of a building’s prior inhabitants. And besides, there was digging to be done.

Torn packaging was everywhere; drugs were one of the first things to get looted. The pills on the floor looked like store-brand stomach medication, but much of it had been ground to chalk under the careless feet that had preceded her own.

Amongst the trash was an unopened prescription bag, half trapped under the pile of shopping carts. She tugged at the bag and it refused to move. She put her flashlight in her mouth and worked with both hands to pull it out, but the bottle in the bag was caught fast. She pressed her foot under the edge of the cart, pulled and with a soft rattle of pills, the bag came free.

But the force of the pull sent the carts tumbling over, crashing to the hard floor in a deafening clatter. Becca held her breath for a moment and covered her ears. Loud noises were never a good thing, even inside. The rumbling banging continued, even after the carts ceased to move and Becca became aware of a sound to her right.

One of Them had crawled out from some dark recess and now was very aware of the intruder’s presence. How long had it been there? Had a back door come unblocked? Were there more? There was no time to find out, it was already stumbling towards her.

Becca stashed the unidentified medicine into a pocket and backed up, only to be blocked by the remains of the shopping cart pile. She did not want to fight it, fighting was not her job. Her job was to Run. She jumped over a toppled shelf to her right and ran up the aisle as the Thing moaned and slogged after her. The path to the stairs was clear and she bolted up and slammed the door behind her. A nearby chair-leg jammed through the handle would be enough to stop one, at least for a while.

She took out the chalk and wrote clearly: “SUPPLIES: MINIMAL, HOSTILES: 1, TAKE CAUTION” and turned to go back to the roof.  Her job was not done, there was room left in her backpack and a city full of wreckage to dig through. She would be busy for a while yet.

She straightened her pack and climbed back out into the world.