It sounds horrific. A girl is raped and imprisoned by a man, who keeps her in an underground cell, with the boy who's a result of the rape. How could this possibly be a moving and intelligent film? But it's brilliant. Everything I've read from the director, Lenny Abramson, and the writer, Emma Donohoe (adapting her own book - not an easy job, in this case) suggested that they'd gone about this in a careful, sober way, without any attempt to shock or titillate.

And so it proves. The central relationship, between the mother and the boy, is brilliantly acted, and the second half of the film - after they escape, moving into the outside world, in a very different setting - is equally rivetting, and not the anti-climax that it might have been. Parents and children, from all sorts of angles (the mother goes back to stay with her mother), and not just the quirky "locked up by a madman" scenario. It's varied, convincing, always worth watching - don't be put off. It's terrific.