It is an unlikely premise for a German novel: Hitler returns to Berlin and gets mistaken for a look-alike. After nearly seventy years in a coma, he is surprised by the way the modern city looks. Where have all the Russian soldiers gone? And why are there so many cyclists wearing flimsy helmets with holes in them?

He looks for his favourite newspaper, the People’s Observer, but it doesn’t seem to be on the stand – only Turkish papers. The shop owner befriends him and lets him in: “Don’t steal anything, OK?” “Do I look like a criminal?” “You look like Hitler”. “Exactly” responds the Führer.

Eventually, Hitler gets into the swing of the modern world and becomes a celebrity and a politician. He goes on a chat-show (hosted by a German of Turkish background) and goes into politics, striking a popular chord with his proposals to get tough on dog mess.

It is a story which has captivated Germany. Er ist wieder da (He’s back) has already sold 400,000 copies. The audio version, too, is a best-seller. Translations into 28 languages are on the way. So is a film.

The appeal is well worn, that of a throw-back from a previous age trying to cope with our own times – Rip van Hitler, as you might call him, is baffled by computers and mobile phones and all the paraphernalia of Berlin today.

But this is difficult territory. Hitler as buffoon is a joke as old as Charlie Chaplin. But Hitler as human being also makes many uneasy. The reviewer, Cornelia Fiedler, of the Süddeutsche Zeitung, attributed the book’s success not to its literary quality but to an unsettling obsession with Hitler. “A very strange fixation on Hitler has developed in Germany and it has something of the manic about it. The focus on Hitler – be it as a comic figure or as the embodiment of evil – risks washing away the historical reality”.

‘Do you agree with him?’

The book’s scenario is absurd – farcical – but author, Timur Vermes, said that he had painted Hitler as a human figure precisely to make today’s Germans have to think hard about him. The plot is far-fetched but the character is human and complex, not the usual portrayal of Hitler as monster or clown.

Vermes told the BBC: “We have learnt over more than sixty years that Hitler was a bad person. But by learning this, we don't think that he did anything that made sense.

“He was elected and people don't elect idiots. We are used to thinking that he wasn't able to think clearly and have a certain kind of logic. I think that is the surprise in the book is that Hitler has a certain kind of logic.

“It's Hitler speaking. You know what he says. It's him and you have to take a stand. Do you agree with him?”

But some critics are troubled by this. They fear Germans might start to feel comfortable about Hitler. It’s a thin line between humanising him in an absurd situation and making him seem like a sympathetic figure. As the critic, Daniel Erk, put it in an interview with the American Jewish magazine, Heeb,: “The humour of the book stems from the fact that Hitler is someone from a completely different time which is interesting because there are both perpetrators and victims that are still alive”.

All of this is now being debated in Germany. Attitudes have changed, according to Rudolph Herzog, who wrote a study called Dead Funny: Humour in Hitler’s Germany. “The first reaction after the war was to say he was a demon. That is saying that he was like a hypnotist who hypnotised everyone so we're not really responsible. The hypnotist is responsible.

“That makes it even harder to answer why this whole thing happened if you’ve got this clownish person and everyone follows his orders to catastrophe. I don't buy that. I really don't buy that at all”.

But that view changed too. A much more nuanced history became accepted, one where the German people were too fully involved.

Comedy on the edge

The singer Thomas Pigor, who plays Hitler’s voice in a very popular animation (which shows Hitler as a figure of fun in the bath with ducks), explained how attitudes have changed since he first started depicting the man: “In 1993, it was really taboo. It was breathtaking for the audience. They asked ‘can we joke about Hitler? Is it allowed to joke about Hitler?’”

Now, it is less shocking. After the war, it was possible to laugh about Hitler too – there was a comic play called I was Hitler's Moustache. “Then we had 1968,” says Thomas Pigor. “The younger generation blamed their elders for the denial of the Nazi past and at this time it was impossible to joke about Hitler”.

But attitudes changed: “In the 70s, we had the American TV series Holocaust. It was an important step because there was Auschwitz in German living rooms from the point of view of the victims. We had Schindler’s List and there was a discussion in Germany about whether it was permitted to treat this theme with a Hollywood format.

But now, with the passing of time, Hitler is fair game for laughs again, says Thomas Pigor.

There are people, though, who say that the only acceptable humour has to be dangerous. It has to test sensibilities.

Oliver Polak is a stand-up comedian who plays with fire. He is Jewish and plays on his Jewishness – he isn’t a German comic who happens to be Jewish but a German comic who highlights his Jewishness.

He calls one of his routines “Das Judenspiel” – the Jew Game. In it, he calls out a series of names and gets the audience to shout back: “Jude” or “Normal”. It’s rather an eclectic list – Steve Jobs, Jesus, SpongeBob. Each time, the audience responds. Then he offers himself as the subject. The audience – in Germany, remember – shouts: “Jude”. He whips them up so that they end up shouting “Jude, Jude, Jude” – “Jew, Jew, Jew”.

Then he comes in with the punch, shouting back: “No, I’m normal. I’m just doing it for the money”.

The atmosphere is invariably electric. Sometimes people leave. Others accuse him of feeding anti-Semitism. He told the BBC he doesn’t know why people laugh or why he finds it funny. “It’s not my job to analyse myself. That’s for my mother or my psychiatrist”.

For him, there can be no comfortable humour about Hitler. He thinks the novel by Timur Vermes is exactly that kind of safe comedy which he dislikes.

Germany, however, loves it. And it is coming soon to a bookshop near you in pretty well whatever language you speak.