Davis came to immunology from physics and, like visions of outer space, his picture of the human immune system—the little we actually know of it—is dizzying, intriguing, and strange. It was only circa 1989 that we began to realize and explore the complexity of how the body fights disease, and this book is as much the story of the science at work as it is what the research has revealed. Davis takes us into the minds of the pioneering biologists as well as into their labs, highlighting what led to various discoveries, from the initial puzzle of how immune cells know what foreign particles to attack (germs, not food; but only harmful germs, not beneficial parts of the body’s microbiome), to whether, and then how, the immune system can fight cancer. But even before investigating the mysteries of auto-immune diseases and the effects of stress, sleep, and age on the immune system, how do scientists choose what questions to ask? When do they pursue “curiosity-based” rather than hypothesis-based projects? How do they design studies? How do they recognize true discoveries—and if they make one, how do they know what to do with it next? Emphasizing that “no scientist is an island,” Davis follows the strings of achievements and failures (always at least as valuable as the successes) that have led to radical reinterpretations of how the immune system works. His explanations are rich in technical detail, but always clear: as he recreates the revelatory moments in the labs, he puts the reader right there at the microscope, on the edge of discovery. I was surprised how quickly I became (temporarily) fluent in the language of dendritic cells, receptors, cytokines, and so on. Davis also clearly defines more familiar terms such as interferons and interleukins, explains cortisol’s effects and how it’s related to cortisone, and flags the truly revolutionary insights in this history of sometimes baffling eureka moments.