Hannah Blane and Colin Masters lived by one single creed: trust. Working together in close proximity, separated from viral death by mere millimetres of protective clothing, they had come to trust each other completely. So when the order came down from the central building they knew exactly what to do. In the antechamber inside the BSL building they went through the safety checklist with meticulous care. Hannah Blane was the first to remove her watch, placing it, with her pens and anything else that could snag on insulating material, in a locked drawer. Colin Masters watched her do this, then did the same under her watchful eye. Both scientists switched off their mobiles before they went anywhere near the hot zone.

After transitioning through the airlock from Level 3, they crouched low as they approached the workbench, bending their knees, before standing up straight inside their protective suits, their faces and bodies sealed airtight with oxygen supplied through a flexible tube attached to their hoods. As an added precaution, they each wore GSR respirators with two filters, one on either side of the head. When they were ready to begin, Blane and Masters faced the solid, transparent Perspex wall that separated them from the live samples inside the core of the lab and slowly inserted their arms into the polythene arm sockets, flexing their fingers inside two pairs of nitrate gloves that could only be worn for thirty minutes at a time before needing to be changed. As a further safety measure, the lab was kept at negative air pressure from the corridor outside, reducing any possibility of an escape of vapour outside Level 4. Next door, watching proceedings on the closed-circuit TV, several SSAs – senior scientific advisers – and a woman from the Joint Biosecurity Centre stood waiting to report back the findings to Whitehall.

Blane and Masters worked in almost total silence, speaking only when necessary. Their mission was clear: to identify the molecular composition of the pathogen as quickly as possible, just as they had with Novichok, Ebola and SARS-CoV-2. To do this, they needed to analyse the genome sequence by examining the genetic structure of the virus and trying to work out where it had come from. The reported sudden deterioration that afternoon in the condition of their source patient, Sheila Mackenzie, had lent an extra urgency to their work. Word had come from London that she had briefly lapsed into unconsciousness before being given a powerful dose of adrenalin and brought round again. The virulence of the pathogen the scientists were handling was in no doubt: both knew there was no margin for error.