'The Reader' leaves an imprint on your mind long after the credits have rolled, the lights have gone up and the popcorn has been cleaned off the seats. Like the tannin residues staining a tea cup, it refuses to be washed away.

Troubling and morally ambiguous, it toys with your established notions of right and wrong, demands empathy where it is righteously inexcusable and leaves you feeling just a little bit soiled.

Adapted by David Hare from the novel of the same name by Bernhard Schlink, the story focuses on the burden of guilt carried by the German nation; the weight of atonement and the blurred line between legality and morality. It offers very few answers and this, whilst it may be viewed as a flaw by some, is what makes so effective.

Superbly directed by Stephen Daldry ('Billy Elliot'), 'The Reader' showcases acting talent rarely stumbled across in the reams of celluloid churned out by the Hollywood machine. Aside from the magnificent performance by Kate Winslet (who really, truly, deserves her Oscar nod), youngster David Kross brings depth to a complicated and difficult role, while the ever-fabulous Ralph Fiennes conveys decades of suppressed pain and shame in a single glance.

Spanning four decades, 'The Reader' tells the story of Michael Berg (first Kross and later Fiennes) and his relationship with a woman called Hanna Schmitz (Winslet). At the age of 15, Michael is seduced by Hanna, a beautiful but lonely woman double his age. Their relationship revolves largely around sex (and a warning for those who may be offended: you see plenty of it) and books. In exchange for his sexual education, he reads to Hanna from the various books he is studying at school. And then, one day, Hanna suddenly disappears.

We next see Michael eight years later (1966) when he is at university studying law. As part of his course, he is taken by his professor to watch the proceedings of a war crimes tribunal in Heidelberg. One of the women on trial for the murder of Auschwitz prisoners, an ex-SS guard, is none other than Hanna Schmitz.

As Michael struggles to come to terms with this revelation, his own feelings of guilt by association and his secret connection to the woman, he realises that Hanna is harbouring another secret, which is, to her, far more shameful than that for which she will face life imprisonment.

Whilst gripping, it is not a particularly easy film to watch. More than that, though, it is not an easy film to forget or even fully comprehend. It does not, however, follow that it is not a film worth watching. Quite the opposite, in fact.