What is it like to be a brain surgeon? How does it feel to hold someone's life in your hands, to cut into the stuff that creates thought, feeling, and reason? How do you live with the consequences of performing a potentially lifesaving operation when it all goes wrong? In neurosurgery, more than in any other branch of medicine, the doctor's oath to "do no harm" holds a bitter irony. Operations on the brain carry grave risks. Every day, leading neurosurgeon Henry Marsh must make agonizing decisions, often in the face of great urgency and uncertainty.