This is a story about Nelson Mandela, and it begins on Robben Island in 1974. Prisoner number 466/64 is writing up his life story, working all night and sleeping all day.  Finished pages go to trusted comrades who write comments and queries in the margins. The text is then passed to one Laloo Chiba, who transcribes it in ‘microscopic’ letters on to sheets of paper which are later inserted into the binding of notebooks and carried off the island by Mac Maharaj when he is released in 1976.

Outside, the intrepid Mac turns the microscopic text into a typescript and sends it to London, where it becomes the Higgs boson of literary properties, known to exist but not seen since it passed into the hands of the South African Communist Party, or SACP, in 1977. Years pass; the mystery deepens. Mandela goes from being an obscure South African prisoner to possibly the most famous living human, subject of global adulation and a ghostwritten autobiography that sells 15 million. His cult is such that prints of his hands are sold for thousands, and yet the prison manuscript stays missing. Until last week, when Professor Stephen Ellis of the University of Leiden sent out an email saying: ‘You’ll never guess what I’ve just found in the online archive of the Nelson Mandela Centre of Memory.’

So yes, the lost manuscript has come back to us and, with it, a range of fascinating questions. Why was it not published earlier? Why did it surface now? And above all, what light does it shed on Mandela’s Awkward Secret, first reported by Professor Ellis in 2011?

Everyone thought Mandela was a known entity, but he turns out to have led a double life, at least for a time. By day, he was or pretended to be a moderate democrat, fighting to free his people in the name of values all humans held sacred. But by night he donned the cloak and dagger and became a leader of a fanatical sect known for its attachment to the totalitarian Soviet ideal.

When Ellis first aired this theory, it read like a Cold War thriller, but when Mandela died last month, the African National Congress and the SACP both issued statements confirming that it was true: at the time of his arrest in 1962, Nelson Mandela was a member of the SACP’s innermost central committee.

This, then, is why Ellis and I were dizzy with excitement when the prison manuscript turned up last week: here was a rich new source of virgin material to be scanned for the smoking gun, the inside and untold story of Mandela’s secret life as a communist plotter. Alas, the smoking gun was not there. But the prison manuscript does offer insights into the manner in which Mandela’s image has been manipulated over the decades.

It is common cause that the ANC decided in the 1960s to use Mandela as the anti-apartheid movement’s official poster boy. He was the obvious choice, a tall, clean-limbed tribal prince, luminously charismatic, married to the telegenic Winnie, and reduced by cruel circumstance to living martyrdom on a prison island. All you had to do was cleanse him of the communist taint and Bob’s your uncle: four decades down the road, you have the president of the USA getting weepy as he describes Mandela’s lifelong struggle for ‘your freedom, your democracy’. There’s no accounting for taste, but one wonders if Barack Obama would have said that if he’d known his hero batted for the opposition during the Cold War.

‘I hate all forms of imperialism, and I consider the US brand to be the most loathsome and contemptible.’

‘To a nationalist fighting oppression, dialectical materialism is like a rifle, bomb or missile. Once I understood the principle of dialectical materialism, I embraced it without hesitation.’