The German lesson.

Siggi Jepsen (the first-person narrator), an inmate of a juvenile detention center, is forced to write an essay with the title "The Joy of Duty." In the essay, Siggi describes his youth in Nazi Germany where his father, the "most northerly police officer in Germany," does his duty, even when he is ordered to debar his old childhood friend, the expressionist painter Max Nansen, from his profession, because the Nazis banned expressionism as "degenerate art" (entartete Kunst).

Siggi, however, is fascinated by Nansen's paintings, "the green faces, the Mongol eyes, these deformed bodies ... " and, without the knowledge of his father, manages to hide some of the confiscated paintings. Following the end of World War II, Jepsen senior is interned for a short time and later reinstalled as a policeman in rural Schleswig-Holstein. When he then obsessively continues to carry out his former orders, Siggi brings Nansen paintings that he believes to be in danger to safety. His father discovers his doings and dutifully turns him in for art theft.

When forced to write the essay on "The Joy of Duty" during his term in the juvenile detention center near Hamburg, the memories of his childhood come to the surface and he goes far beyond the "duty" of writing his essay by filling several notebooks with caustic recollections of this entire saga. - Wikipedia