Every year dozens of books on the history of South Africa are published worldwide, concerned with foreign influences on the development of South Africa's state structure, politics, and culture. Great Britain, the Netherlands, Germany, France, Portugal, and China immediately come to mind. Yet few people know what a significant role another country – the Soviet Union – played in the events that make up the history of South Africa in the twentieth century. Irina Filatova's and Apollon Davidson's book The Hidden Thread: Russia and South Africa in the Soviet Era opens hitherto unknown pages on the relations between South Africa and Soviet Russia and offers the reader a fresh look at the recent history of these countries.

Filatova and Davidson have long studied the history of South Africa and authored books on this subject both in Russian and in English, among them the two-volume South Africa and the Communist International: A Documentary History and two recently published books in Russian: Russia and South Africa: Three Centuries of Contacts (2010) and Russia and South Africa: Building Bridges (2012). The most recent book, which is reviewed here, is a unique study of the ties between South Africa and Russia, starting in the seventeenth century with the first mention of ‘Moscovy’ in the journal of Jan van Riebeeck, the founder of the Cape Colony, and ending in the twenty-first century, when South Africa and Russia both became members of BRICS (a political and financial consortium of emergent economies convening Brazil, Russia, India, China, and South Africa). The authors pay particular attention to the Soviet era – from the 1917 revolution to the breakup of the USSR. Despite the fact that for most of this period there were no diplomatic relations between the two countries, it was at that time that Russia's influence on South Africa was the most significant, as the Soviet Union was right at the centre of the struggle against apartheid.

The early chapters of the book describe the reactions of South African communists to the Russian revolution. In the Soviet ideals of equality between classes, nations, and races, many of them saw an ideology that was the exact opposite of the official ideology of their government. On the basis of archival material only recently available to researchers, Davidson and Filatova recount the unlikely history of the activities of the Communist International in South Africa. It will be a revelation for many readers to find out that the Communist Party of South Africa (predecessor of the present South African Communist Party) was in fact a branch of the Comintern.

The authors explore the influence of the Soviet Union on the African National Congress (ANC). The official policy of the ANC and the views of many of its leaders were in many ways connected with and even based on Soviet ideology. Without downplaying the ideological side of the relationship between the ANC and the USSR, the authors stress that the decisive element in this relationship was Soviet military support for the ANC's armed struggle. Its methods of waging guerrilla war, its organisation, and its propaganda, particularly in the 1980s, were modelled on the Soviet course in military combat work, which was taught to almost all ANC fighters in either the Soviet Union or in Angola by Soviet military advisers. Without this influence, the kind of armed struggle that was waged in South Africa in the late 1980s would not have been possible and the ANC would not have been able to project itself as the main organisation fighting apartheid inside the country.

Historians have long disputed whether the late Nelson Mandela was a member of the South African Communist Party. The authors for the first time demonstrate that Mandela was not only a member of the SACP, but also a member of the Central Committee that made the decision to begin the guerrilla war. Another surprising discovery is the direct link between the Soviet KGB and South Africa's National Intelligence Service (NIS). This led to a visit by two Soviet intelligence officers to South Africa in 1987. The NIS hosted the visit and organised the Russians' meeting with P. W. Botha. This revelation comes from several former NIS officials interviewed by the authors.

In the late 1980s, the Soviet's partnership with the ANC came under stress. Many among the Soviet elite began to lean towards establishing relations with the National Party, which caused unease in the ANC. The final chapters of the book are devoted to political and diplomatic relations between South Africa and Russia in the 1990s and 2000s. The authors also discuss the reasons for the negligible trade between the two countries and their slowly developing economic ties. They also throw some light on Russian-associated crime in South Africa.

The Hidden Thread will undoubtedly give rise to arguments, particularly with the passing of Nelson Mandela. This applies both to the facts claimed by the authors and to the interpretation they offer of them. Readers may disagree with their judgments on the Soviet role in South Africa's twentieth-century history. The events described in the book are recent and people are still passionate about them. Many archives in Russia and South Africa remain closed, so there is room for continued re-evaluation. But for now Filatova and Davidson's remarkable and provocative study is unique both in depth and scope and is bound to remain so for a long while.