This is an extraordinary story of how Nazism seemed to a child, and what it did to the rest of her life. During Katrin Thiele's childhood in Nazi Germany, with a father in the SS and "a beautiful stainless steel swastika badge" to pin on her youth-group uniform, she says that "it was the only time in my life I had no doubt that I belonged."

When the American conquerors arrived, the badge was buried in the garden. But, "my memories of Nazism were an integral part of my childhood and most of them were happy." She became "a confused and closet Nazi", still devoted to the ideals she had absorbed, such as self-sacrifice and dedication to duty.

This book is her self-exorcism. It is brutally honest in a way that I think most Germans living in Germany would find imposssible. For the paradox is that, for most of her life, Katrin has been English, and so has her family. At the wartime reception after a German cousin's wedding, everyone did the Lambeth Walk, even though Hitler had banned it. She conveys, with remarkable recollection, just how things seemed to a bright eight- year-old, more interested in dolls' houses than in ideology.

How did she end up in this tangle of nationalities? Her German grandfather, a hairdresser, had settled in late-Victorian London and married her English grandmother. The First World War destroyed their lives. He was interned; his wife was forced to conceal her marriage. After the war, he was expelled to Germany, and his wife followed. Their daughter was Katrin's mother.

Seeking refuge from the disasters of the Weimar republic, the grandparents became ardent Nazis. Katrin's mother also married an early Nazi. Yet, in some sense, they all remained English. The grandparents always spoke English to each other, and went in for English foibles such as knitted tea-cosies. With the war's end, most of the family got back to England. But "Papa" was abandoned, a symbol of a dead Germany. Katrin was given an English surname, and lived in dread of "exposure as a German".

Some of the most touching passages concern her attempt to make sense of her days as "Papa's little girl". "Though the fate of the Jews under Nazism has since emerged as by far the most significant issue of the regime," she writes, "from the perspective of a child growing up in Germany at the time it was a minor issue." Yet what would an SS Oberleutnant, who fought in Russia, have got up to? She tracks down the evidence of one massacre, and satisfies herself that he wasn't guilty of it. But can she have overcome other doubts?

Reinvented as an English schoolgirl, Katrin went up to Oxford and was interviewed, in 1955, by Iris Murdoch. "Why do you want to study philosophy?" Miss Murdoch wondered. She fell about laughing when Katrin said: "I want to be wise." But this brave, moving and notably well-written book is also a very wise one. (Virago , pounds 16.99)