A bunch of teenagers become convinced that their neighbor, a police officer, is the serial killer reported to be active in the area, and launch a recon mission. A bit familiar, perhaps, but stay with it and you’ll be rewarded. What seems like a cookie-cutter YA thriller gains interest and urgency as it unfolds. Each time they’re sure it’s him, a new clue renders their convictions ambiguous. Keeps you guessing. So not exactly trail-blazing, but a competent, effective teaser that’s refreshingly earnest and honest. Personally, I hated the out-of-sync ending that left a bad taste and the shameless sequel setup. (105 min)