Meet Tristan Hart, a brilliant young man of means. The year is 1751, and Mr Hart leaves his Berkshire home for London to lodge with his father’s friend, the novelist and dramatist Henry Fielding, and study medicine at the great hospital of University College. It will be a momentous year for the cultured and intellectually ambitious Mr Hart, who, as well as being a student of Locke and Descartes and a promising young physician, is also, alas, a psychopath. His obsession is the nature of pain, and preventing it during medical procedures. His equally strong and far more unpredictable obsession is the nature of pain, and causing it. Desperate to understand his own deviant desires before they derail his career and drive him mad, Tristan sifts through his childhood memories, memories that are informed by dark superstitions about faeries and goblins and shape-shifting gypsies. Will the new tools of the age—reason and science and skepticism—be enough to save him?