Sinister is a horror movie about a writer (Ethan Hawke) who wrote one bestselling true crime book, and has spent the rest of his adult life chasing the fame he once had. Ellison has carted his long-suffering family with him from crime scene to crime scene, trying to find another murder story that will make the public care about him again. And as the movie begins, he thinks he's gotten his big break. After moving his family into the house where another family was recently killed under bizarre circumstances, he's discovered a treasure trove of old Super 8 movies in the attic. All of them feature horrific family murders. But that's actually the least interesting part of the movie, though it is probably the scariest. The best part is something you'd never anticipate.
Very light spoilers ahead.
There are a lot of things that Sinister writer Robert Cargill and director Scott Derrickson got right about making a good horror movie. First of all, they invented a new monster, the Babylonian deity Bagul (yes, I could hear people in the theater around me making Ghostbusters jokes about Zuul), who starts out looking sort of like the Wicked Witch of the East and winds up looking legitimately disturbing. More importantly, they also came up with a convincing reason why Ellison doesn't go to the cops as soon as he discovers the snuff movies in his attic. That's right — this is a horror movie that uses character development to justify actions that most horror movies never explain. (For example: "Why does he go up the stairs instead of calling the police?" etc.)