It’s one of the world’s great detective stories: the hunt for the cause of AIDS – the worst plague since the Black Death. One of the strongest theories is that an experimental polio vaccine involving monkeys in central Africa led to the virus being passed on from animals to humans. Recently the two main protagonists in this debate met face-to-face for the first time. Dr Hilary Koprowski, the man who headed the vaccination programme in Africa in the 1950’s & Ed Hooper, a journalist who after 9 years of investigation says that Koprowski’s vaccination was responsible for AIDS. We speak with both men.