This is one of the most compelling Holocaust stories I have read. In 1943, Marianne Strauss, a 20-year-old German Jew from a wealthy Essen family, runs out of the house as her parents are being rounded up. Instead of going into hiding, like Anne Frank, she tints her hair red to make herself conspicuous and acts out a new life as a vivacious German widow who has lost her papers in the Allied bombing. Marianne Strauss braved out two years on the run with chutzpah, courage and a strong sense of political consciousness.

This is one of the most compelling Holocaust stories I have read. In 1943, Marianne Strauss, a 20-year-old German Jew from a wealthy Essen family, runs out of the house as her parents are being rounded up. Instead of going into hiding, like Anne Frank, she tints her hair red to make herself conspicuous and acts out a new life as a vivacious German widow who has lost her papers in the Allied bombing. Marianne Strauss braved out two years on the run with chutzpah, courage and a strong sense of political consciousness.

However, it is not just her story that is fascinating, but the way that Mark Roseman tells it. He never writes as an impartial observer, but allows his analysis to inform the story. This sense of the author as modern commentator lends to a picaresque history a very special importance.

Roseman, professor of modern history at the University of Southampton, gives the detailed background of Marianne's parents, their bourgeois lifestyle and identity as Germans rather than Jews. He shows how the family's deep confidence in German values, and their over-assimilation, gave them a false sense of security. Ironically, it was this bond that helped Marianne to live - because she identified totally as a German, she could hide out as one.

Roseman argues that Marianne survived only because she was able to adopt several identities simultaneously. She was a Jew who had escaped the Gestapo and who sometimes pretended to be a politically endangered Aryan. At other times, she posed as an ordinary German widow. Even more bizarrely, she occasionally masqueraded as an agent of Hitler. In later life she admitted going into train compartments where senior Nazis and Gestapo officers travelled. Whenever anyone asked her what she was doing, she replied: "I can't tell you because I am under direct orders of the Führer."

By constantly reinventing herself, Zelig-like, she survived. Roseman presents a picture of a fiercely idealistic woman who, at the end of the war, joined the Communist Party. However, she fell in love with a English Orthodox Jew. Roseman hints that, by marrying into a conservative, provincial Jewish family, Marianne became a bourgeois housewife and lost her spirit as a freethinker and radical. Apart from the tragedy of losing her daughter to anorexia nervosa, not very much is known about her life in Liverpool. She died in l996.

Roseman has also unearthed vital historical material. Why was the Strauss family protected briefly by the Wehrmacht's counter-intelligence organisation, the Abwehr? Roseman hints at corruption and bribery. He also reveals the existence of Izbica, a little-known Polish concentration camp where Marianne's fiancé was incarcerated. Perhaps most important is the news of a secret organisation, the Bund, where Jews and Aryans worked against the Nazis. This was not the well-known Jewish Bund, but a socialist resistance movement, with roots in dance and gymnastics, that aided Jews, half-Jews and Nazi opponents fleeing the Gestapo.

Marianne was sad never to have succeeded in getting members of the Bund recognised as "righteous gentiles", but Roseman's fine excavation should help to make up for this neglect. This book has just won the Fraenkel Prize in Contemporary History awarded by the Wiener Library: it is a great work.

Julia Pascal's new play, 'London Continental', is at the Arcola Theatre, London E8, until 5 November