(Sorry if Scott's Mom is wildly out of character. It's been a while since I watched season 1 of Teen Wolf and I don't recall her being that prominent in any episodes anyway.
This is in Teen Wolf season 2 and some magical part of Supernatural after season 4 but before the end of season 8. Probably closer to the season 8 side, but before Cas flew over the cuckoo's nest. But basically, spoiler warning for all of supernatural, just to be safe.)
Melissa McCall had been called a lot of things in her life. Wife, Nurse, Mom. But "Crazy" was not something she was accustomed to. So when Melissa was walking home from work one night and saw a normal looking teenager transform into a… creature, she started to wonder whether or not her sanity was completely intact. She could have brushed it off as a trick of the light, until it started coming towards her, eyes glowing and teeth snarling, like a savage wolf.
She screamed and began to run, but she could feel it gaining on her. She tripped and fell to the ground, bracing herself for sudden death, when suddenly another creature tackled the first to the ground. It was too dark to make out anything but the rough shape of two savage beasts attempting to tear out each other's throats. While the two monsters were distracting each other, Melissa ran for her life. She made it to her doorstep and shakily thrust her keys in the lock.
"Scott," she called out once she was inside, almost afraid to make her voice go above a whisper. She quickly locked the door and paced through her house. Scott is with Stiles, she remembered. Probably playing video games. He won't be home for a couple hours. I should call animal control. But then she thought about the near attack, and about how the figure had seemed so human. No, she decided, this is something bigger. I have to call my brother. I have to call John.
They were sitting at a diner, about to dive into two pieces of the most delicious looking pie Dean had ever seen, when the phone began to ring.
"It's not me," Dean gargled as he stuffed two consecutive bites of pie into his pie-hole.
"It's not mine either," Sam murmured as he pulled his phone out of his pocket. "Hold on a sec."
Sam dug through his many pockets until he found the phone. The two stared at each other.
"That's Dad's phone. The one I went dumpster diving for after that Boy Scout in your body dumped it," Dean remembered.
"Hello?" Sam asked into the phone as he caught it on the final ring.
"John?" The voice was female, unknown.
"No, John is unavailable right now. Who is this?"
"I really, really need to speak to John. This is Melissa, his sister."
Sam choked a little on the saliva in his mouth. "His sister?"
Upon hearing this, Dean began choking on the three spoonfuls of pie stuffed in his mouth.
"Yes. He told me to call him if I ever had a… a certain kind of problem."
"Like?" Sam had a feeling he knew where this was going.
"I don't really feel comfortable talking to a stranger about this. Can you just have John call me back as soon as possible?"
"I'm sorry to say, but John Winchester is dead. He died a few years ago."
There was silence on the other end as the news sunk in.
"He… died?" The woman was very obviously distraught.
"Yeah, I'm sorry. My, associate and I, we worked with John on everything. Anything he could have helped you with, we can help."
Dean shot Sam a warning look.
"Can you hold for just one second?" asked Sam, as he put his hand over the receiver.
"She's Dad's sister. We have to help her," Sam argued.
"Then why have we never heard of her? Are you completely forgetting what happened with Adam?" Dean insisted.
"Adam was real. It was just the ghoul that wasn't. And maybe if we get to this Melissa woman first, nothing bad will happen to her like it did to them."
Dean rolled his eyes, but Sam took his silence for consent.
"Sorry, I'm back. Anything, and I mean anything, you need, we can help you with," Sam spoke back into the phone.
"This is going to sound really stupid but, do you believe in monsters?"
(This is just a prologue. You people decide whether or not it finishes. If you like the idea, please review and tell me. If no one seems interested in it, I won't bother writing it. I just sort of mashed this out to get the idea on paper. If I start writing the full story, the quality of writing should be much better)