On an uncobbled road, in the cold grayscale of night with naught but the pale moon to guide her, a lonely shape walks onward and skirts the Everfree Forest.  Her movements are slow, deliberate, and planned, not betraying any sense of her motives nor identity, for she covered her body in its entirety in a long, black shawl.  On top of a gradually approaching hill, amidst the silver glow of starlight, lay a very small town flanked only by thick plots of agriculture.  With a chilling breeze at her back, the unicorn glanced up at the first building nearby: candlelight flickered gently behind the single pane window.  With the twilight of daybreak only four hours away, something was definitely wrong, and with the current state of affairs of the world she figured it would be safe to investigate.

It didn't take long to close the gap between herself and the house: her movements were so precise and deliberate that, when given a reason for conviction, she seemed to travel supernaturally fast.  She gazed into the window, looking in at a very quaint room without much luxury, and at a young male pony lying in his bed.  He was dead, she knew it, but she needed to get closer in order to feel for the perpetrator.  She had hoped very dearly that the current problem hadn't spread this far into barely settled land, but the blood stain on this poor colt's nose was indication to the latter.  She leaned forward, using her hoof to flick her hood back just enough to expose her horn, then touched it to the window and sealed it until it was air tight.  The unicorn then stepped around to the front door, not a very far walk of course, and tested it.  The door was locked, but even the most complex locks still relied on basic mechanical operation: she leaned down, looked inside, and let her magic do the work.  Each of the pins within the lock moved itself, while the bolt spun of its own accord.  Slowly but surely the pins separated, dropping into place and allowing the cylinder to be inched ever closer to freedom.  Finally, the last pin clicked and the lock opened, granting the unicorn access into the small farmhouse.  As quickly and quietly as she had approached, the cloaked figure made her way to the colt's room.  With only four rooms or so, this wasn't exactly difficult to do.

The unicorn found the doorway that she wanted and pushed on it, irritatingly enough it too was locked.  She didn't particularly care for finesse at this point, though, so she used her magic to force it open.  The crunching of metal and wood was probably the loudest thing that sleepy little town had heard in quite some time, and the unicorn detected rustling from the other major doorway in the house.  She did not care, however, and made her way calmly and deliberately into the bedroom.  The scent of blood wafted through the air, but was rapidly overpowered by the stench of death as soon as the still environment was disturbed.  The unicorn stepped forward to the edge of the bed, looking down at the bloodied figure and using her hoof to remove the old quilt that was lying on top of him.  The thing made a sickening peeling noise as it separated from his body, revealing that his chest had been torn open, or rather eaten open, and that his heart was indeed missing.  There was no sign of the perpetrator.

The silence of the room was very quickly disrupted by the colt's parents barging over toward the open doorway.  They moved so quickly that, when they stopped at the threshold they very nearly extinguished the burned-down candle on the colt's dresser just from the change in air pressure.

"Who are you?  What are you doing in our house?"  The stallion yelled into the room, holding his foreleg around his wife who stared on in disbelief at the cloaked figure.  The instance they realized that their son was wounded, though, they forsook anymore questions.  "What did you do to my boy!?"

"Calm down."  The unicorn spoke from beneath her hood, turning halfway so that she could face the enraged parents.  The stallion whispered to his wife to go fetch his pitchfork, which she did with absolutely no hesitation.

"I don't know who you are or what you're doing here, but you had better start explaining yourself this instant!"  As he finished his yelling, the light blue mare returned with his rusty old pitchfork.  The stallion grabbed it and viciously prodded it in the cloaked unicorn's direction just to make his point more clear.

The unicorn smirked.  In the dim light of a single candle, the two earth ponies could only see the flash of her teeth beneath the hood.  To his surprise, however, the pale yellow stallion's pitchfork started to bend almost by itself.  The forks at the end tilted upward in a ninety degree angle, flaking off bits of rust and making a horrific grinding sound as it did so.  He dropped the tool, though it didn't fall where he expected it to: it turned and flew toward him and his wife.  They both flinched, still already shocked by the apparent murder of their son, but the teeth of the pitchfork found their way only into the doorjamb, extending the wooden handle across the doorway like a stop arm.

"I'd advise you not to step into this room until I'm done here.  I did not kill your son, but I know who did.  Well... what, rather."  As she spoke in her calm and unperturbed voice, the unicorn turned her head back to the colt's body.  To the parents' horror, she reached her hooves down to the cavity in his chest, spreading it open with a crunching of ribs and a squelching of half coagulated blood.  "Oh, and to answer your question,"  She flicked her head back, letting the hood drop down onto her withers as she worked, revealing her scarred and weathered face to them.  She turned to look the parents in the eye, still holding her hooves inside of their sons' chest, but smiling once more as if she were exchanging pleasantries over tea.  Her left eye had a very unique scar on it, one akin to a tree tough it was slightly incomplete: like a failed brand attempt.  Her throat had a great deal of stitching going down it, and she was covered in small, unhealed (though not bleeding) wounds.  The parents could tell that this unicorn was at one point very attractive, but she seemed as if she'd seen wars unspeakable.  Her purple hair and faded magenta highlights fell down as they exited the hood, and her pale lavender coat barely reflected any light at all.  It was as dull as her cold, glazed eyes.

"You may call me Umbra, and I'm afraid you have a rat problem."  With this, 'Umbra Noctis' telekinetically pulled a group of small rats out of the boy's chest.  Each one writhed and squirmed, hissing and snapping their jaws in her direction to express their 'displeasure' at being pulled out of the body by their tails.  The parents looked on in terror at the little brown creatures, and were rendered speechless as the purple unicorn produced a small, ancient pewter dagger embossed with an ornate sun and sliced off all of their heads at once.  Their bodies didn't fall to the floor, though she did release them, but instead they burst into flames, burning away until not even ash remained of them.

The speechless, quivering and crying parents couldn't tear their eyes away from the very wounded unicorn, even as she walked back toward them.  She didn't need, nor want, for them to speak to her, though, so she made her point very clear.  "I got all the rats, so you can cremate his body.  Oh and be sure to wash yourselves very thoroughly with lemons after you step into the room.  Every inch.  There's a terrible plague going around...  You really don't want to catch it."

Umbra proceeded to rip the pitchfork out of the wall and drop it on the floor.  The parents stepped out of her way as she walked past, leaving the premises of their house and walking off into the night.  The light blue mare fell to the floor, as did her husband not long after, and they sat at the threshold, staring blankly into the room with tears rolling down each of their cheeks.

As the mysterious stranger walked in through the back woods town, she could see signs of the infestation: torch sconces pillaged, bits of hay and other dried goods stolen and left as a fallen trail into back alleys and sewers, rats scurrying about, both of the magical and nonmagical variety.  She was needed here, but in truth she was needed all over Equestria.  The best case scenario by that time was genocide: the question was whether it would be of the ponies or of the rats.