Sophie

The darkness could not hide her feral grin.
Stumbling back over the treacherous forest litter, the boy couldn't disguise the horror he felt at what his best friend had become.
"What's the matter, Bobby?" The girl crooned, her head tilting sideways like a curious bird even as fur sprouted from her face. "I thought you liked monsters."
"So- Sophie," Bobby could barely get her name out, let alone beg her forgiveness. This had been his idea, after all.
His idea, and now his fault.
"Sophie, Sophie." Her name sounded so menacing as Sophie's teeth lengthened into fangs. "That's not really a good name for a monster, now is it?"
"You're not a monster." Bobby shook his head in denial, though the guilt in his gut mocked his lie. He tripped on something and hit the ground.
Sophie laughed, the sound a discordant blend of bitter and gleeful. "Aren't I? Isn't that what we were trying to do with that stuffy old book; summon monsters?" She spread out her arms, and a glint of the full moon's light shone on her new claws. "Congratulations, Bobby. It worked."
"It wasn't supposed to!" There was a whine in his voice, one that made Sophie's now yellow eyes gleam hungrily. "And it didn't say anything about it possessing one of us!"
"Who would have attempted the ritual if it had?" She asked, voice roughening into something more guttural. "Leave enough mystery to such things, and soon the cats will come. And you know what curiosity does to such creatures." There was hunger evident in her voice now.
Bobby stared at the creature that looked less and less like his friend with each passing moment. Was Sophie even still in there? (Oh, Bobby hoped not. Hoped his friend wasn't trapped with that monster, unable to do anything but watch it control and steadily transform her body.)
"Sophie never could say no to one of you little adventures. Her heart was so sweet with its love for you." The monster bared its teeth in a farce of a smile as it stepped forward, testing Sophie's legs. "I wonder, how will yours taste on her lips?"
The monster lunged, and Bobby's scream sounded through the forest before abruptly dying.