Bruno Pontecorvo was the father of neutrino astronomy and a brilliant nuclear physicist who disappeared through the Iron Curtain at the height of the Cold War.

Why did he flee so suddenly, was he a brilliant spy as well as a physicist, and what secrets did he take with him to the Soviet Union?

Professor Frank Close of Oxford University tells the story, from his new book Half Life and reveals the role of the infamous traitor Kim Philby in the affair.