Taking us inside the ongoing quest to use phages' powers for good, Tom Ireland introduces us to the brilliant, often eccentric, scientists who have fought to realize phages' potential in the face of doubt and political intrigue. We meet the renegade French-Canadian scientist who discovered phages and pioneered their use as medicine over a century ago, leading them to be hailed as the world's first genuine antibiotic years before penicillin. We learn why, in some pockets of the former Soviet Union, drinking a vial of phages remains as common as taking an over-the-counter drug. We follow the intrepid scientists and doctors now racing to make "phage therapy" work worldwide as the threat of antibiotic-resistant bacteria grows ever more urgent--even as other researchers uncover how phages bolster our everyday immunity, help generate the oxygen we breathe, and furnish the origins for breakthrough technologies like CRISPR.