For some reason, teenage and pre-teen girls have become the new action hero. It can only improve the genre, despite the poor use to which Joe Wright puts Saoirse Ronan in this contrived, overwrought splat of arty hackwork. As the relentless tween assassin of the title, she glows like a towheaded changeling, conveying a wild child's feral wonder at such things as fluorescent lights whenever she isn't snapping necks or outrunning wounded caribou. Trained by her father (Eric Bana) in their sub-Arctic refuge, she's let loose on a mission that involves vacant lots in Berlin and a CIA handler (Cate Blanchett) who demonstrates her wickedness by brushing her teeth until her gums bleed and by collecting shoes. Never content with an arresting image when he can overwhelm it with a rotating camera and a blast of music from the Chemical Brothers, Wright takes a taut, brainy, Salt-like thriller and turns it into an exercise in faux irony and metaphor.