Five bored high school senior girls are planning a party for their friend Colby, who doesn't seem too excited about it. The credits give these girls names, but the film doesn't. Instead, they are identifiable as the bitchy alpha blonde, the sad sack with an eating disorder, the airhead in pigtails. Their toxic dynamic is reminiscent of the cliques in "Heathers" and "Jawbreaker," and a slow-motion shot of the girls dressed in dark colors, walking in a pack, is even a little like "The Craft." Director Chris Rubino, the title designer behind some of the most popular indie ventures in recent years ("Blue Valentine," "The Place Beyond the Pines"), keeps the action and focus squarely on the girls: their faces, their expressions, their reactions. As their perverse plan reveals itself, watching them becomes unsettling. They're just a little too relaxed, a little too calculating, a little too casual, a little too happy. They’re so pretty and they’re so cruel. Screenwriter Ruby Rae Spiegel, (author of critically acclaimed play "Dry Land"), deftly excises passages from the Donald Barthelme story on which the film is based to use in a voiceover. Cinematographer Reed Morano's ("Vinyl" on HBO) moody palette perfectly captures the darkness lurking beneath the picturesque, tree-covered small town where the action is set. All of which calls into question where, exactly, the titular “threat” lies. -Elizabeth Logan