Since March 2022, the world has experienced the COVID-19 pandemic. Imagine more than 400 years of the bubonic plague that devastated Europe in the Middle Ages. We thought we knew its causes. In The Black Death: New Lessons from Recent Research, medievalist Dorsey Armstrong robustly describes plague biology, correcting inaccurate pandemic explanations. COVID-19 isn't likely to be humanity's last experience with a zoonotic disease. What can we learn now from these two pandemics?