Born Monster by Rachel Howard

Growing up, Lily lived alone with her serial killer father who taught her how to prey on her own victims. At the age of eighteen, Lily lost her father to the court system. To honor his legacy, she decides to continue the massacring of dozens of citizens. To ensure her safety, Lily’s father asks Caleb, a family friend to keep an eye on her. Instead, he loses his daughter to an inner monster no one ever knew was there

When Caleb shows up in Lily’s life, Lily instantly falls in love. It starts with a serial killing partnership. The love and romance mixed with the adrenaline of killing innocent people are intoxicating. However, as her craving grows out of control, Lily’s father catches wind of it and sets out to end her spree by hiring an outside hitman.

On the run, Lily and Caleb have to work as a team to make it out alive. The only problem is that once the main hunter is dealt with, Lily becomes the huntress. The monster inside of her overpowers any emotions she has ever felt. Lily loses all connection to humanity and becomes something that even serial killers are afraid of.