Sienna Mercer Sienna Mercer grew up in Toronto, Canada. She was an only child, and always wanted a brother or sister - especially a twin. A twin would have been awesome! Sadly, she never got that sister so, when she was grown up, she did the next best thing - she wrote stories for girls about a girl who reminded her of herself, and gave her the most fun, fabulous twin she could imagine . . . a vampire twin.