This is one of those films where the less you know about it the better, although it may be hard to avoid the details given how many awards the film has been racking up lately.
What I will tell you is that the Sugar Man of the title is Sixto Rodriguez, an American singer songwriter, who in the early 70's made a couple of records that were roundly ignored in his home land, and everywhere else, with the exception of two countries. He had a moderate amount of success in Australia (although this isn't mentioned in the film) and became a phenomenon in South Africa.
That Rodriguez was as big as the Beatles in South Africa was something that he didn't know about, and South Africa knew very little about him. All they knew about him was that he was American and he committed suicide by setting himself on fire on stage during a performance.
A dedicated fan in South Africa started his own dogged investigation into the mysterious Rodriguez, which is where Searching for Sugar Man begins its bizarre and wonderful journey. It's a journey that touches on race relations in both countries, the cut throat and corrupt nature of the music industry and the power that music has to transport and inspire. Mostly though it's a portrait of a truly unique individual.