I always worry when movie makers try to adapt a good book for the screen, knowing there’s a good chance they’ll screw it up. In the case of “The Reader,” however, I needn’t have fretted.

Bernhard Schlink’s  excellent novel raises difficult questions about responsibility for Nazi atrocities and the guilt that has afflicted post-war generations of Germans. The book is well-served by Stephen Daldry’s  direction, David Hare’s  screenplay — and especially by Kate Winslet’s  mesmerizing performance.

Winslet plays Hanna Schmitz , a thirty-something trolley conductor in late  1950s Germany. When she discovers a very ill teenage boy vomiting outside her home, she cleans him up and sees him home. Months later, when young Michael Berg has recovered and returns to thank her with a bouquet of flowers, Hanna repays the courtesy by relieving him of his virginity. They begin a mutually rewarding affair: He reads to her from literary masterpieces; she initiates him into the crafts and pleasures of lovemaking. The summer-long romance ends when Hanna abruptly vanishes.

Flash forward to the mid-1960s . Michael and a small group of fellow law students attend the trial of six wartime concentration camp guards. To his surprise, Hanna is one of them. She acknowledges having been a guard and having condemned certain prisoners. But, to preserve a key secret about herself, she confesses to an act she did not commit. Michael knows she is innocent, but doesn’t inform the court.

Hanna becomes a prisoner of the state. Michael becomes prisoner of his mind, tormented by memories of his romance, anger and sadness at his erstwhile lover’s crimes and guilt for not revealing the information that could have lessened her sentence. Perhaps not surprisingly, his post-Hanna relations with women are less than successful.

The narrative seesaws in time, with Kross as a besotted youth and later as a law student, and Ralph Fiennes  portraying the adult version of Michael. Kross captures both the glow of carnal bliss and the anguish of discovering that his lover might have been a monster. Fiennes is superb as the deeply saddened and emotionally repressed grown-up Michael. Lena Olin  has only one scene, but it’s a spellbinder. She plays a concentration camp survivor who helped expose Hanna and the other guards.

But “The Reader” mostly belongs to the expressive Winslet, who makes an indelible Hanna even though Hare’s screenplay (and Schlink’s novel) tell us little about her past and what goes on inside her head. If Winslet’s work in “The Reader” doesn’t earn at least a nomination at Oscar time — it would be her sixth against no wins — then something is terribly wrong in Movieland.