Their affair lasts a summer - over time, Michael feels more attracted towards his school mates and is torn between his feelings, but always goes to Hanna. One day, she is gone without a word. The feeling he has betrayed her with his school mates never goes away.
He meets her years later in court. Michael is a law student following a process of concentration camp guards. Hanna is accused for deliberately joining the SS and not having saved women from a burning church where they were locked in on their journey from Auschwitz to the west. Hanna confesses everything, which is then misused by the other accused women. They say Hanna was the leader of it all and wrote the report. When the judge wants to take an handwriting test, Hanna admits she indeed wrote the report.
It is then that Michael realizes that Hanna is illiterate and ashamed of that fact. So ashamed, that she'd rather spend the rest of her life in jail than to admit she can't read nor write, which would be enough proof she couldn't have written the report. Michael is torn again: should he talk to the judge or even to Hanna and try to convince her to tell about her handicap? He decides not to.
Michael has two big problems with Hanna and her past. First, he feels guilty for her deeds as a concentration camp guard because he has loved her. I think this is difficult to understand for non-Germans. German people, especially those living short after the war, bore a great weight of collective guilt on their shoulders. Loving someone who had been in the SS almost meant the same as having been in the SS yourself (at least, that's how Michael feels).
Second, he reproaches her for what she had done to him: after their affair and her sudden leave, he never was able to have a functioning relationship again. He compared all his partners with Hanna and she always took part in his life. His marriage only lasted four years. When Hanna was in prison for a couple of years, he started to record tapes for her, reading aloud the books he loved. It was this ever presence in his life (and her leaving him without a word, giving him the feeling he had treated her wrong) that he accuses her of, too.
I think this novel is rather difficult to understand at first glance. It is a short novel, only 200 pages, but you have to dive into Michaels world view to really understand him. The writer writes beautifully, but doesn't give the reader all the information; you really have to do some work with the book and maybe even give it a second read.