A new BBC film dramatises the adventures in 1930s Berlin of the English novelist Christopher Isherwood. Earlier adaptations of his Berlin stories, including the musical Cabaret, helped shape the popular idea of what Berlin was like as the Nazi-era loomed. But how true to life have these versions been?
Christopher Isherwood arrived in Berlin in 1929. He had recently abandoned his medical training in London and had published a not very successful novel. At 24, he knew he needed a new direction - and by the time he left Germany in 1933, he had found the material to make his name as a writer.
His semi-autobiographical stories of pre-Hitler Berlin have been influential, firstly on the page and then reworked by others as a play, a stage musical and on screen.
Isherwood went to Germany to be with his friend, the poet WH Auden. The two young men, both gay, were seeking intellectual stimulus but they also hoped for more physical diversion. As Isherwood recalled much later: "To Christopher, Berlin meant boys."
"Auden's father had offered to pay for his son to have what we would now call a gap year. He chose Berlin, I think, because of the sexual atmosphere," says Professor Norman Page, who has written a book about the two writers' time in Berlin.
"No doubt he wrote excited and exciting letters to Isherwood urging him to join him. Auden went home but Isherwood stayed almost four years and never really lived in Britain again."
Inspiration from life
Christopher Isherwood was planning a long novel about Berlin life to be called The Lost. "But as a writer he was a sprinter, not a long distance runner," says Professor Page.
So Isherwood published two short works based on his Berlin adventures and acquaintances.
In 1935 came Mr Norris Changes Trains and then Goodbye to Berlin in 1939. The same year he moved permanently to America, where he died in 1986.
He had mined his own life for inspiration more than most writers dare, as the 2009 film A Single Man, directed by Tom Ford, showed. But the afterlife of his Berlin stories has been extraordinary: it is hard to think of another writer whose take on a specific time and place proved so definitive.
In 1951 John van Druten wrote a play based on the stories called I am a Camera. His challenge was to find the dramatic focus.
In the 1930s, Isherwood couldn't write openly about his own homosexuality. So the original stories are linked by a narrator who is always slightly out of focus, with readers left to draw their own conclusions. The most famous line is: "I am a camera with its shutter open, quite passive, recording, not thinking."
But 20 years after Isherwood's Berlin adventures, the stage play is less honest about his sexuality than the originals had been. A suddenly heterosexual Isherwood has a relationship with nightclub singer Sally Bowles.
In real life there had, of course, been no such affair but Isherwood explained there had been a real Sally Bowles, a young Englishwoman in Berlin called Jean Ross.
As he wrote her, Sally's main talent is for snaring wealthy older men.
Jean Ross died in 1973 having said little about being used as the model. In reality, Ross was a political radical who went on to have a relationship with the author Claud Cockburn.
His son, Alexander Cockburn, knew her much later. "Jean was a wonderful woman, warm and gentle in demeanour. She couldn't have been more unlike the rather tinny character portrayed in Sally Bowles. She was extremely intelligent, politically alert and vital. She probably found the portrait painted by Isherwood rather irritating."
Ross may have been annoyed at Isherwood's invention but the success of Jan Van Druten's 1951 Broadway play I am a Camera (filmed in 1955) meant the writer was now losing control of his own creations.
Later he said the regular arrival of cheques soothed his wounded self-regard.
In 1966, the play became the hit musical Cabaret. Six years later came Bob Fosse's massively successful movie version, starring Liza Minnelli.
Professor Norman Page says by this time little resemblance remained to the "real" Sally Bowles. "In fact near the end of his life Isherwood admitted he couldn't really remember what Jean Ross had been like. The memories had been overlaid by all the actresses who played her various reincarnations," he says.
But, he says: "In all their different versions his stories and characters evoke a crucial period in European history - even if what we learn about the realities of '30s Berlin is quite limited. His picture is rather sanitised - Berlin was a place of great hardship and suffering but you don't see much of that."
Professor Page says changing literary taste will keep the stories alive. "Isherwood operates in an area which has become more interesting to us in recent years: the frontiers of fiction and autobiography and the whole nature of truth-telling in fiction."
Forty years after leaving Berlin, Isherwood revisited the territory again not as fiction but in his memoirs Christopher and His Kind. "It was the '70s and the whole public atmosphere had changed," says Norman Page. "He could come clean."
The city Isherwood wrote about always had an element of invention. But even now when we imagine the Berlin of the early 1930s, part of what we see is Christopher Isherwood's Berlin.
Christopher and His Kind is on BBC2 on Saturday 19th March at 21.30