The remarkable true story of a team of doctors who – through years of scientific sleuthing and observant care—discover a surprising connection between opioids and memory, one that holds promise and peril for any one of us. How could you lose your memory overnight, and what would it mean? The day neurologist Jed Barash sees the baffling brain scan of a young patient with devastating amnesia marks the beginning of a quest to answer those questions. First detected in a cluster of stigmatized opioid overdose victims in Massachusetts with severe damage to the hippocampus—the brain’s memory center—this rare syndrome reveals how the tragic plight of the unfortunate few can open the door to advances in medical science. After overcoming initial skepticism that investigating the syndrome is worth the effort—and that fentanyl is the likely culprit—Barash and a growing team of dedicated doctors explore the threat that people who take opioids chronically as prescribed to treat severe pain may gradually put their memories at risk. At the same time, they begin to grasp the potential for this syndrome to shed light on the most elusive memory thief of all—Alzheimer’s disease. Through the prism of this fascinating story, Aguirre goes on to examine how researchers tease out the fundamental nature of memory and the many mysteries still to be solved. Where do memories live? Why do we forget most of what happens in a day but remember some events with stunning clarity years later? How real are our memories? And what purpose do they actually serve? Perhaps the greatest mystery in The Memory Thief is why Alzheimer’s has evaded capture for a century even though it afflicts tens of millions around the world and lies in wait for millions more. Aguirre deftly explores this question and reveals promising new strategies and developments that may finally break the long stalemate in the fight against this dreaded disease. But at its core, Aguirre’s genre-bending and deeply-reported book is about paying attention to the things that initially don’t make sense—like the amnestic syndrome—and how these mysteries can move science closer to an ever-evolving version of the truth.