Beginning with the "occasional miracles" of a mysterious turn-of-the-century cancer vaccine called Coley's toxins, Stephen S. Hall traces the story of how doctors have learned to use the immune system and its "commotions," as one physician put it, to develop a wide array of cutting-edge therapies. Traveling between laboratory and bedside, Hall's absorbing narrative navigates the politics of discovery and explains the dazzling complexities of human blood, tracking the potent molecules and powerful cells at the heart of the immune response. As Hall proceeds across continents and time, he discusses interferon, tumor necrosis factors, and the newest and most promising substances to trigger a "commotion," such as interleukin-2.