Nowadays, governments are quick to enlist the media in their efforts to highlight the perceived threat posed to world security by the leaking of sensitive documents to rogue states such as Iran and North Korea. Most countries that possess nuclear technologies have long-established security networks in place that aim specifically at controlling and preventing the illegitimate transfer of information and expertise. Their efforts are publicly lauded as exemplars of effective policy making designed to frustrate those regimes seeking to destabilize peace and democracy. But, as Simone Turchetti reveals, this was far from the case at the dawn of the nuclear age.

In October 1950, Bruno Pontecorvo and his family disappeared during a holiday in Finland. Since Pontecorvo was known to be working for the UK Atomic Energy Research Establishment at Harwell, his apparent defection to the Soviet Union when Cold War tensions were at their height would today have caused a sensation. After all, it was only five years since the Second World War had been bought to a conclusion by America's use of atomic bombs on Japan, and the time of the Berlin airlift, the start of direct confrontation between the new superpowers in Korea, and communist insurgencies in Malaya and Indo-China. However, the newspapers were strangely slow in asking the obvious questions. Was Pontecorvo in possession of classified information? Had he passed secrets to the Soviets? Was he a spy? Was he a communist? And the silence from Whitehall was deafening.

Turchetti treats us to a clear, well-balanced analysis of an unfolding affair. We learn why difficult questions were largely fudged or left unanswered. Yes, Pontecorvo was the first and only scientist employed in the Second World War nuclear projects who, in the 1950s, crossed the Iron Curtain. An expert in both pure and applied physics, he was also someone whose knowledge was recognized far beyond Britain, not least for the fact that he had collaborated with prominent scientists in the wartime United States nuclear programme. Therefore his disappearance would have only compounded the anxieties that existed over the lax practices of those charged with the defence of atomic secrets. But it is the lack of pretension involved in Turchetti's framing of Pontecorvo's worth to the Soviet Union that sets the tone for a sober measurement of the affair's significance in the overall historical trajectory of the Cold War. Diplomats, security officers and government officials in both Britain and the United States are revealed to have colluded in their accounts of the various agencies involved in the affair in order to accommodate national political and economic interests. Add into the mix contested patents with tens of millions of dollars at stake, neatly interwoven with links to pacifism and subversive political activism, and Turchetti gently leads to an appreciation of the wider contemporary ramifications and long-term consequences of the affair.

The author obviously not only has researched widely and deeply across the relevant fields, but also continually challenges himself to delve further into the nuances of the arguments his research exposes. It is only a minor grumble, but the narrative does get bogged down in details over the production of fissile materials for atomic weapons. Nevertheless, this book deserves its place on the reading list of both scientists and historians of the twentieth century.