Raised to survive and adapt in the Nordic wilderness by her CIA-exile father (Eric Bana), lethal teenager Hanna (Saoirse Ronan) is ready to come out of hiding. Her decision puts them both back on the radar of his ruthless former handler (Cate Blanchett), leading to a deadly game of cat-and-mouse during which all are determined to tie up loose ends from the past. While bearing the marks of many a trained-killer thriller, Atonement director Joe Wright frequently goes off road to make it a relentlessly intriguing and exhilarating ride.
Essentially it's Bourne goes to film school as Wright puts his quiet assassin through her paces in various situations lifted from the coolest Euro-thrillers of recent years, from Run Lola Run to Luc Besson's deadly duo Leon and Nikita.
Whipping up a more immediate furore to the one she created in Atonement, Saoirse (say "Seer-sha") Ronan is the freakishly gifted adolescent brought up as a hunter-gatherer-ninja in the snowy wilds of Finland by her ex-CIA spook father Erik (Bana).
Framed for the death of Hanna's mother by his former handler Marissa Wiegler (Blanchett), Erik has spent 15 years preparing Hanna for her return to civilisation.
He also ensures that when the day comes, Wiegler knows all about it. So no sooner are they back on the radar than the woods are crawling with CIA troops who find Erik gone and a defenceless girl alone in the shack.
At least she looks defenceless...
Of course it's all part of a meticulous plan that takes Hanna on a transcontinental journey of violence, vengeance and self-discovery.
For the first half-hour, Wright and co-writers Seth Lochhead and David Farr play a gripping blinder.
But after building to an early crescendo, they loosen the tenterhooks with a misguided side-step into comedy, hooking Hanna up with a travelling English bubblehead (Tamara Drewe troublemaker Jessica Barden) and her new-age parents (Williams and Flemyng).
At the same time, Weisler enlists a wildly camp associate (Hollander) to join the hunt, his viciousness matched only by his fondness for 80s leisurewear and giggling like a B-movie Nazi.
As far as suspense is concerned, it's a case of too many quirks spoil the broth. The film's quest for metaphors and convenient plot drivers also leaves a few holes in Hanna's education.
So while making her deadly in combat and fluent in umpteen languages, Erik puts more importance on Grimm fairytales (she's an innocent in a cruel world, see) and space-race trivia (she's like the dog Laika who was launched into orbit with no chance of return) than the rather more relevant concept of electricity.
Television baffles her. But curiously she has no problem mastering the internet. Hmm.
Skipping through the forest of credibility like lethal red riding hood, Ronan takes each Gilliam-esque lurch from comedy to tragedy to surrealism in her stride.
And, Schwarzenegger accent notwithstanding, Bana adds clout in the screen time he's given. Blanchett, however, does little more than regurgitate her icy villainess from Indiana Jones 4 with a deep South drawl.
Energised by a pounding soundtrack from the Chemical Brothers, the action is impressively staged, peaking with Hanna's thrilling escape from CIA clutches and Erik's despatching of half a dozen goons in one neck-snapping long shot.
Hanna's not always on target, but you shouldn't take your eyes off her.