I almost cheated and put a portion of the climactic chapter where the fairly untrained heroine engages the antagonist in hand to hand combat in a sewer with a three foot piece of rusted rebar, but I decided against that and and went with part of the prologue:
The shadow slides up his hoodie, wrapping itself almost lovingly around his torso. He shivers involuntarily. As the shadow closes around his neck, the tingle of unease at the back of his mind blossoms into full-blown panic. He sprints, desperately making for his apartment and the safety of a locked door.
A sudden clamping of the shadow forces all the air from his lungs in a whoosh. Jacob collapses, falling face first into the road. The unyielding asphalt scrapes painfully against his face, but he doesn't notice as his body now feels likes it is on fire. The creature's tendrils sink into his chest to wrap around his heart and squeeze. His mouth and lungs work in a futile effort to draw breath.
In its haste to feed, the monster let its grip go slack. The pressure redoubles with a rib-cracking crunch. Spots appear before his eyes. His oxygen-deprived limbs begin to convulse despite the monsters efforts to keep him still.
Jacob thrashes soundlessly against the asphalt, but quickly his efforts begin to slow. The blood pools in his limbs and then spots dance before his eyes.
Jacob stares upward. The stars, normally dim spots in the city lights and smog, shine brilliantly in his field of vision before everything goes blissfully dark and quiet.
After a few minutes, the shadow moves again. It glides silently over the sidewalk and down an alley, a fine dust rising in its wake.
It needs some work. The original idea had this in the second person, which wouldn't work for the YA story I'm writing, and so the flow and grammar still needs some work.