On 14 June 2006, police were called to 9 Downshire Hill in Hampstead. The owner, Allan Chappelow, was a writer and notorious recluse who had not been seen for several weeks. Inside the darkened house, officers found piles of rubbish, trees growing through the floor, and the body of Chappelow, battered to death, partially burned and buried under four feet of paper.

The man eventually arrested on suspicion of his murder was a Chinese dissident named Wang Yam, who claimed to be the grandson of one of Mao's closest aides. His trial was the first in modern British history to be held `in camera': closed, carefully controlled, secret. Wang Yam was found guilty, but has always protested his innocence. 

Did Wang Yam do it? Or was he framed for a crime he didn't commit? When everything is hidden, how do we know what's really true?