Two things are making Kate Winslet feel weird. One is talking to the chap from The Times about the role she’s playing while she’s playing it – something she swore she would not do. The other is that, as we talk, at the back of a courtroom constructed in a town hall in suburban Berlin, a Kate Winslet lookalike is standing in for her while the camera rolls on one of her fellow actors.

This is not how Winslet likes to work. The other actor is playing a judge, and it’s vital for him to be able to react to the real her, she says. Art demands it. So does fairness – he was there for her the day before when they shot the scene from the opposite angle.

There is a reason for the unfairness – it takes an hour and a half for Winslet to get through hair and make-up and the production can’t wait; but, in the end, she can’t stand it any longer. She strides off to stand in for her stand-in and delivers every line as if her life depended on it.

An hour or so later, we’re on to the next scene, the one for which her hair has been moulded into a metallic-looking helmet and her face aged to 44. It’s a pivotal moment in a complex, heart-rending story, The Reader, that has become embedded in the German psyche after a decade in print, and has been translated into 39 languages. In it, Winslet must convey unimaginable mental torture, while hardly moving or uttering a word.

An assistant director asks for silence, and the very large number of people milling around the building oblige. Stephen Daldry, the director, does two takes. Winslet stays in character between them. For about eight minutes she inhabits another life that she has spent weeks imagining in every detail, a life defined by dark secrets, and quite unlike her own. After the second “cut” she exhales and hangs her head. Daldry comes over and massages her shoulders. I scribble in my notebook: “This is what they’re paid for.”

Months later, Daldry is in his edit room off Times Square in New York, and is actually amused by this bovine reaction to a moment of extraordinary artistry, which will doubtless feature in awards-show highlights coming our way soon – The Reader is already being talked of as an Oscar contender. In fact, he almost agrees. “She certainly gets paid for going into an emotional state, and, first of all, understanding what the character needs to do,” he says. “In other words she has a huge intellectual facility, but married to a huge emotional facility that is just fearless.”

As a film, The Reader lost all three of its original producers and nearly failed to make it to American screens this year because of a showdown between two of Hollywood’s most powerful moguls. As a novel, by the Berlin law professor Bernhard Schlink, it has sold nearly one million copies in the US alone, and not just because of an endorsement from Oprah. It tackles, in the style of a detective story, the unbearable German dilemma of Holocaust guilt, as felt by those who acquiesced to it and as inherited by their children.

The reader of the title first appears as a teenager drawn into an affair with an older woman, played by Winslet, who is working as a tram conductor. She then disappears without explanation – at least until the teenager, grown up (and played by Ralph Fiennes), is stunned to see her in the dock at a major postwar Holocaust trial. He is left to wonder how he could have loved her, and whether he has compromised himself in doing so. He is also mystified, almost to the end, by her true motivation. The book has been criticised as too willing to humanise the generation condemned by the historian Daniel Goldhagen as “Hitler’s willing executioners”. But it is also on school and college reading lists from Leipzig to Los Angeles.

Filming it was always going to be a big deal. If this were a British story, it would have been expected to find a British director. But, being German, for reasons of national self-confidence (or lack of it) and the primacy of the English language, the equivalent assumption didn’t hold. “I’m sure there were many German directors who stepped up before me to say, ‘I want to make this,’” Daldry says, “but, in the end, that decision was Mr Schlink’s, and he actually chose Anthony Minghella.”

Minghella bought the rights but did nothing with them, so Daldry started badgering him. They agreed that David Hare would write a script, that Minghella would switch to being a producer, and that Winslet should be their first choice for the central role of Hanna Schmitz, one of a group of female guards accused of letting hundreds of Jewish women die in a church fire. Schlink also agreed, but Winslet was busy starring in Revolutionary Road, directed by Sam Mendes, her husband. So Daldry turned to Nicole Kidman (she had won an Oscar as Virginia Woolf in Daldry’s The Hours). Kidman signed on, but then fell pregnant. Daldry went back to Winslet, who by this time was free. All he needed now was a male lead. He cast Ralph Fiennes.

Thus did the most talked-about German novel in a generation acquire a British producer, director, screenwriter and starring line-up. For good measure, Sydney Pollack and Scott Rudin, Hollywood legends both, joined Minghella as producers. Never let it be said that German nationalism lives on in the movies. Schlink and the German actors cast in The Reader’s smaller roles have – so far – expressed nothing but gratitude for the chance to work alongside an Anglo-Saxon A-team. Their careers all stand to benefit, not least because of the sheer weight of expectation that is about to settle on Kate Winslet’s shoulders: she has been nominated five times for an Oscar, but never won.

With so much riding on a film, you might expect the tension on set to be palpable. There is a hint of it. When Daldry is coaxed away from the camera for a pre-booked chat with me he is a mite distracted. (Q: “What do you hope will give this film its broad popular appeal?” A: “I’ve no idea.”) Otherwise, the whole operation feels like a well-catered drama workshop.