It’s the whodunnit – or whatdunnit – that has kept scientists, politicians, journalists and armchair sleuths speculating ever since the first stories of a ‘mysterious viral pneumonia’ began leaking out of Wuhan: where did Sars-CoV-2, the virus that causes Covid-19, come from? Was it an unlucky natural occurrence, a bat virus which made the opportunistic leap from animals to humans somewhere in the pulsing zoonotic stew of a Wuhan wet market? Or did it stem from the accidental infection of a laboratory worker, most likely in the nearby Wuhan Institute of Virology (WIV), which by 2019 had collected nearly 20,000...