Sophie is the hidden villainess of "Can You Keep a Secret?", the 4th book in R.L. Stine's revived Fear Street series (published on April 12, 2016).
Sophie was the younger sister of protagonist Emmy, whom she was very close with. But unbeknownst to Emmy and the siblings' parents, Sophie was harboring a secret: she was a werewolf, having been attacked by one as a child and transformed. Her powers first emerged a few months prior to the book's events and, during the course of the book, Sophie began attacking and killing animals in Shadyside. She also began manipulating her sister into believing she were a werewolf, which was aided by Emmy having recurring nightmares of Sophie in her werewolf form, but believing the dreams to be of herself. She was also aided by her half-blind Aunt Martha, who comes to stay at their home for a few days and tells Emmy that she had been bitten by a wolf in childhood (mistaking her for Sophie). Midway through the book, however, Sophie also killed Emmy's friend Riley while as a werewolf.
In the climax of the book, Sophie helped Emmy and her boyfriend Eddie Kovacs in breaking into the office of Eddie's boss Mac Stanton (the owner of a local pet cemetery) and retrieve the money he had stolen from them, which had been stolen from an armored bank truck and hidden in a tree of the Fear Street forest that Emmy and Eddie found. When Mac caught the three teens, he took them out to the cemetery and forced them to jump down into a hole filled with animal carcasses, shoving Sophie into the hole first. Soon after, Sophie began to transform into her werewolf form, revealing her villainous secret to Emmy and Eddie. After jumping out of the hole and mauling Mac (though he ultimately survived), Sophie returned and explained how she had discovered her "wolfen" powers and used them to make Emmy believe she was the werewolf instead. She also cruelly blamed Emmy for her being transformed and that she'd manipulated Emmy out of jealousy of her being able to live a normal life. Regarding Riley, he had witnessed Sophie transform back into her human form after killing a dog, and she killed him to keep him quiet. She then leaped out of the hole and ran away, ignoring Emmy's pleas for her not to. But at the end of the book, Emmy returned home and found Sophie there with their parents, calmly eating plums and claiming to have been at a friend's house during the events at the cemetery. Once the girls were back in their bedroom, Sophie told Emmy she had decided she didn't want to live in the forest like an animal and that she'd continue living at the house--as long as Emmy could keep her secret.
- "Because you were normal and I was not. It wasn't fair, Emmy. It was never fair. I was just three years old when I was bitten. You should have protected me. You should have helped me." (Sophie blaming Emmy for her transformation into a werewolf).
- "Why should I be the only one whose life is ruined? Why should I be running on all fours, killing, craving meat like a low animal, while you're totally normal, out having fun with your boyfriend and your friend?" (Sophie showing her bitterness over Emmy being "normal")
- "Can you keep a secret?" (Sophie's final line of the book)