Quammen is a writer who produced several books on scientific topics, lately focusing on pathogens. In this book, he analyses several occurrences of spillover (the ecological process whereby a pathogen jumps from a host species to a new one) via interviews with protagonists and accounts from the field. I guess it became so popular during the latest pandemic (COVID-19) exactly because he talks a lot about how the world we are building, with all the issues due to climate change, loss of biodiversity, unsustainable market demands are creating situations where spillovers can become more likely. It's very well written and researched.