Danny (Li) has been raised as a dog by his "uncle" Bart (Hoskins), a Glasgow loan shark who sends Danny in to cause physical mayhem when clients don't pay up. Danny has flashes of memory from his early life, including a fascination with pianos that, when he's left on the street alone, leads him to blind tuner Sam (Freeman) living with his prodigy goddaughter Victoria (Condon). They adopt Danny and bring him out of his shell, but violent tendencies lurk under the surface. And they'll come in handy if Bart finds him.

The film's sensitive, emotional heart sets it apart from most action movies (except Leon, of course). There's a genuine yearning in Danny that we can identify with--he wants his humanity to triumph over his animal instinct, and he responds strongly when Sam and Victoria show him some compassion. Li plays it well; we feel his struggle to overcome the ruthless conditioning that forms his interactions, grief and rage. Freeman and Hoskins are polar extremes--warm kindness and vicious greed---and both are as watchable as ever for the tiny details they bring to their roles. And Condon has the best character, as Victoria blossoms from an insecure young woman who's spent her life pursuing a musical dream and understands what it's like to have others controlling your life.

The premise is fascinating, and well worth exploring. But Besson isn't interested in a serious study; he has entertainment on his mind, as usual, so it dissolves into big action set pieces in the end. They're bracingly well-staged (the fierce fistfight in a tiny loo is astonishing), filmed with a gritty texture that keeps things looking edgy and alive. There's something endearing about a movie that can be this gruesome and brutal and yet have a centre so thoroughly sweet. And as we discover, sweet is good.