Trusting the audience's intelligence, the filmmakers waste no time with ambiguity over whether Miles is evil or simply misunderstood. Buhler's script is clean and economical, with an inexorable logic to each twist. What's more refreshing is how the scariest moments upend the cliches of the genre. When Sarah goes into labor, for example, a cute puppy watches her and John gather their hospital bag. We suspect that the poor dog will fall victim to Miles' hands, and that it's just a question of when. And that subplot does resolve itself in an exacting, tragic way. But by making the dog's fate more about character development than chills, McCarthy creates an involving scenario that leads to a shattering payoff.