A standard device in detective stories is a map on which certain buildings are circled. Their locations are thought to be revealing, though often they just create a false trail. When four of the first cases of a strange, pneumonia-like illness seen in Wuhan, China, in December, 2019, were found to have a connection to the Huanan Seafood Wholesale Market, it seemed a key to solving the mystery of the illness’s origin. Live animals were reportedly on sale there, offering a route for pathogens to jump from wild species to humans. But then other cases, some of them earlier, were identified, with no known connection to the market. In due course, more sites were circled on the pandemic map. One was the Wuhan Institute of Virology, which contains a Biosafety Level 4 lab. The institute’s work included experiments on the bat coronaviruses that are among the closest known relatives to SARS-CoV-2, which causes COVID-19.