This chapter reflects on the routine and mundane operation of secrecy in the British biological weapons programme. Biological warfare security classification in the UK sat alongside a more general governmental system of security classification and vetting that had grown up during the Second World War. The Canadian concerns reinforce the point made several times so far, that much more was at stake in assigning and harmonising security classifications than the exercise of bureaucracy. In the Los Alamos case, Masco describes a security breach in a secretive atmosphere that generates rumour and gossip; this is then followed up by social control through the emplacement of hypersecurity measures. Paul Fildes, the head of the research programme, and his deputy David Henderson visited the site and attempted to stem the outbreak, apparently by setting fire to heather in the vicinity of the infections.