Half Sister

In a quiet and peaceful suburban town lives a typical family: Brittany Carnation; her parents, Joe and Mary Carnation; and her beagle, Squirt. All her life Brittany has been told she is lucky to be an only child, and she hasn't questioned that. But one stormy day, a girl older than Brittany shows up on her doorstep and claims to be Brittany's long-lost half-sister, Kate. Brittany is confused, and even more so when Joe and Mary seem very uncomfortable. Nevertheless, Joe and Mary invite her into the house to live with them. Kate is very weird, even scary. Eventually the truth comes out: Kate is a half-demon, and the demon side comes from Mary's first marriage four years prior to her marriage to Joe. Brittany is at first outraged at her mom for having a relationship with a demon and for not telling her, but soon she learns that Kate has been sent on a mission from the demon, Tony, to kill everyone in Brittany's family, including Brittany. Brittany now has to face her new mission: kill Kate, while keeping as many members of her family alive as possible.