April 1986: Number 4 Reactor, Chernobyl Nuclear Power Station, explodes, releasing a deadly cocktail of radioactive materials. The fallout reaches Britain three days later, as the world slowly wakes up to the worst nuclear accident in history... Two decades later, four retired British civil servants are found dead. The deaths do not appear suspicious, and the men seem unconnected. Then an old man commits suicide. Before he dies, he sends a document to a young journalist. It reveals a terrifying secret at the heart of Britain's nuclear establishment, a secret people are prepared to kill for. A secret vital to Britain's security. A secret worth billions. Has the government covered up the true effects of the radioactive dust that settled across Britain? And why? Or is the truth far worse...?