Soon after atomic bombs were dropped on Hiroshima and Nagasaki, a black rain containing radioactive materials fell from the sky. No detailed data has ever been released on where this contaminated rain fell, and the extent of this form of radiation. But at the end of 2011, enquiries by a doctor in Nagasaki led to the disclosure that investigators in the 1950s had collected data on some 13,000 people exposed to black rain. Why has this information yet to be released -- 67 years after the atomic bombings? And what might we learn from these cases today? Our investigation includes accounts from survivors.