Hey, Katzentatzen and Ichneumon! Just caught this now, in a bout of narcissistic self-googling. (Or maybe I'm lying and I've been refreshing this page for the last couple of months as I procrastinate on finishing my novel.)
Thanks for reading, I'm glad you enjoyed it.
Sam's book hints that the monster that was Sarah had killed more than just Heather.
Good catch. I tried to leave enough hints so that the reader could figure out the backstory, but I also wanted it to be kind of open for interpretation, because I have commitment issues.