A few months ago Andrew O’Hagan gave a talk in Glasgow to a group of new writers. In it, he encouraged them to be ambitious with their subject matter, and compared the state of fiction in Britain today to that in North America. He lamented how many writers on this side of the Atlantic are shy about tackling big issues, and joked about how he’d recently got into trouble for saying on Radio 4 that ‘every novelist in Britain today is writing about their mammy’. He then gave examples of great past writers who had been unafraid. Charles Dickens, he said, would not have baulked at the idea of setting a scene in, say, 10 Downing Street, even though he hadn’t been there. In his writing he simply trusted his instincts and used his imagination; why were modern writers so afraid to examine their society as Dickens did?

If we look at current authors across the water, it can be argued that the most inspired and most experimental are the most experienced. Chuck Palahniuk’s Rant, a dazzling fake biography in a documentary style, is his tenth book and arguably his best. Philip Roth has nearly 40 years experience now and his hugely popular recent novel The Plot Against America changed one key detail of history and ran with it.

And then there is Norman Mailer. To read Mailer’s books is to convince yourself he has never been afraid of tackling anything. Since his debut The Naked and the Dead (an account of his service as a rifleman in the South Pacific during the Second World War) became a bestseller in 1948, he has dealt with the subjects society is most sensitive about, consistently carrying trouble with him for nearly 60 years, tackling every known literary form that exists with radical, reckless bravery along the way. Mailer spent time in Hollywood writing screenplays, has been interviewed as much as any writer in modern history, contributed brilliant journalism and essays to nearly 100 publications, advised several American presidents and has even run for office himself, in New York. His personal life is equally amazing: five wives, nine children, ten grandchildren.

A small sample of titles of Norman Mailer’s works demonstrates his incredible range. Few others would even attempt anything like Cannibals and Christians, Why Are We in Vietnam?, The Prisoner of Sex, Portrait of Picasso as a Young Man or The Gospel According to the Son. No writer always produces works of genius, but this last title tells us that, as well as dealing with current concerns, Mailer does not flinch at stepping into the minds of some of history’s most famous characters. At the age of 84 he remains as relevant as ever, and with The Castle in the Forest he has chosen to break one more huge taboo.

For my next trick, he says to his readers, I will make you sympathise with Adolf Hitler. Some believe there is little left to say about him – and a quick scan at Mailer’s vast bibliography of hundreds of volumes on the man suggest that might be true – but in this astonishing novel he reminds us not only that there is room for one more contribution on Hitler, but reminds us also how powerful fiction can be. More than that: why fiction is important to historical understanding. No amount of dry factual accounts could do what Mailer does here.

The story begins with a theory. It looks at rumours of Hitler’s supposed Jewish grandfather (was his hatred driven by his fear of being part-Jewish?), then exposes the multiple incestuous relationships in his Austrian family tree; the inference is that this messy gene pool might help explain what made him. There is certainly something in this. The narrator’s account says Hitler’s despicable father Alois married three times, his third wife Klara was also his daughter, herself the product of a one-night stand with his sister Johanna. In her defence, Klara didn’t know this; she thought she was only his niece!

A hundred or so pages pass before Hitler himself appears, but by that time readers are in no doubt what an unusual, unstable, unhappy family he is born into, or the genetic explosion waiting to happen when little one-testicled Adolf is born. Klara’s first three children all died before he was born, so she smothers her new son with love out of fear he will leave her. When little Adi shows signs of surviving infancy she can refuse him nothing. When he rebels she keeps quiet. When he defecates and spreads the results all over the family home, Klara doesn’t get angry, she just cleans up the mess before his father sees it. Again, the author is making a quiet suggestion here: because no one told him not to do so as a child, Hitler grew up to spread his shit all over the world. As the narrator tells us: ‘evil children can issue nicely from the most loving mothers.’

This is quite a beginning, but even at this point the story hasn’t really started. It enters a whole new dimension when the narrator reveals himself; the book is being ‘written’ by an assistant to the Evil One himself, who goes on to explain how he has been under orders to nurture Adolf Hitler, ensuring that as an adult he becomes a full convert to the devil’s side. Now he is ready to tell the story of how it happened. This opens up a whole new spiritual dimension to the novel which introduces a code language used by angels and devils, describing fights between good and evil that show human beings as mere pawns in a bigger scrap to rule the planet.

Norman Mailer agreed to appear in person at this year’s Book Festival but now says the three As have kept him away: asthma, age and arthritis. He will be appearing by videolink though, using Margaret Atwood’s invention, Longpen, to sign books from across the Atlantic. Nobody pretends it’s not disappointing that Mailer can’t be in Edinburgh, but there may not be many more opportunities to see and hear one of the great masters; no doubt the devil himself would approve of anyone trying to beg, borrow or steal a ticket to be there.