Humanity had never reached a technological development like the one we enjoy today. However, the advances of globalization do not guarantee the survival of our species on a planet still dominated by micro-assassins. Viruses, bacteria and parasites make up the biological threat that has accompanied us since the beginning of time. But its epidemic potential represents a new challenge in a hyper-connected and constantly moving world. Emerging diseases, global health alerts, unknown viruses, new species of transmitting insects … Now, the Spanish researcher Pilar Mateo goes through the scenarios where the health of our species is at stake. It is an adventure of thousands of kilometers across three continents in search of micro-killers.