Not the only one //Derek hale x female oc

What happens when Lydia's sister, Cassandra/cassie Martin has a secret. And not the normal kind. This secret pushes her sister away but closer to scott and stiles.

She was just like Lydia until her world was flipped over and upside down. How's she gonna take it?

Read to find out.

TW WILL BE AT THE BEGINNING OF EVERY CHAPTER THAT HAS SOME THAT NEEDS TO BE TW. THANK YOU.