The exact nature of the work undertaken at Sergiev Posad-6 is not something the Kremlin likes to discuss. Nestled in a forest outside Moscow, the military bioresearch laboratory is one of three such sites in Russia to which international monitors have never been granted access. During the Cold War, the complex enjoyed a chilling reputation as a major centre for the Soviet Union’s development of biological weapons, working with the viruses that cause smallpox and Ebola. After the fall of the Berlin Wall, Sergiev Posad-6 went quiet – but, it seems, never entirely silent. Moscow insists any research it conducts…