The Strangling Angel examines the rise and fall of diphtheria in twentieth-century Hamilton, Ontario. Diphtheria causes a white membrane to grow in the throat and obstruct breathing, earning it the name “the strangling angel”. This gruesome disease was once a major cause of death among children in Canada and it persists in many developing countries today. The Strangling Angel sets Hamilton’s experience with diphtheria against the ancient history of the disease, its various disguises, medical efforts to treat and prevent it (sometimes more deadly than the disease itself), and explains how diphtheria became a major threat to public health in Hamilton in the 1920s. This is the story of how cooperation between the people of Hamilton, medical professionals, and path-breaking researchers studying bacteria, led to the elimination of diphtheria from Hamilton, and later, all of Canada.