That last problem is the chief one facing the title character of “Hanna,” a sleek thriller opening Friday, buoyed by smart performances and a director eager to prove his action chops.

As the story opens, Hanna (Saorise Ronan, “The Lovely Bones”) and her father, an ex-CIA agent named Erik (Eric Bana, “The Time Traveler’s Wife”), live in the snowy isolation of Scandinavia. Dad has kept Hanna from civilization and raised her as an expert in survival. She speaks several languages, has memorized encyclopedias and can deliver a serious ass-kicking.

Such skills prove useful when she decides to leave the nest. A former colleague of Erik’s, the icy and cruel Marissa Wiegler (Cate Blanchett, “Robin Hood”), has made it her life’s mission to track down Hanna. What follows is a global chase as the trio cuts zigzag paths before converging at an abandoned amusement park in Berlin.

Feature-debuting screenwriters Seth Lochhead and David Farr offer tantalizing dribbles of information as Hanna and Marissa close in on one another. What is the relationship between the three? What does Marissa want with the girl? And why is Hanna so damned good at killing people?

Along the way, Hanna hitches a ride with a British family touring Morocco. For the girl, who knows her way with a gun but can be overwhelmed by a TV or teakettle, the clan provides a glimpse into a curiously loving world. Hanna develops an affecting friendship with Sophie (Jessica Barden, “Tamara Drewe”), a teenager with decidedly nonlethal preoccupations.

Director Joe Wright packs “Hanna” with wit, style and a clockmaker’s precision. He deftly calibrates between scenes of emotional intensity and visceral action, the latter of which is staged with a rare clarity, given today’s penchant for hyper-editing.

Wright has particular fun with set pieces. In a single, uninterrupted shot, he follows Bana from a bus station to an underground garage, where he is attacked by a group of government agents. It’s an eye-popping bit of filmmaking similar to a stunt he pulled of in “Atonement.” The stylistic flourishes are occasionally excessive; a propulsive score by The Chemical Brothers alternates between exhilaration and distraction.

The movie is not just bells and whistles. Ronan imbues the enigmatic Hanna with an otherworldliness that doesn’t obscure the girl’s vulnerability. Blanchett is delightfully nefarious, while Bana does the most with an underwritten role. And Bardem supplies some welcome humor.

“Hanna” ultimately adds up to something a bit less than its parts, perhaps inevitable when the questions and buildup are more interesting than the eventual revelation. Still, a lot of movies have third-act stumbles, and “Hanna” manages better than most. This is one case of teen angst well worth catching.