McKenna draws on more than 200 interviews and more than 1,100 scientific papers in writing the first book to tell the story of MRSA (methicillin-resistant Staphyloccus aureus), a pathogen that lurks in our homes, hospitals, schools, and farms, and is evolving at a rate faster than the medical community can track it or drug developers can create antibiotics to quell it. McKenna takes readers into the medical centers where frustrated physicians must discard drug after drug as they struggle to keep patients alive. She discloses an explosion of cases that demonstrate how MRSA is growing more virulent while evolving resistance to antibiotics with astonishing speed.