Betrayal, lost honour, guilt and expiation; boundless, consuming, illicit passion; the desire for death and oblivion: such are the ingredients of Tristan und Isolde, a legend of Celtic origin about the tragic love of a knight and a princess. Over the centuries the myth has fascinated writers and musicians alike. According to Friedrich Nietzsche, Richard Wagner made it into an almost metaphysical opera that transcended his own artistic talent, with a score straddling the border between Romanticism and modernity. No only is Tristan und Isolde unparalleled in Wagner's output: its mystery remains impenetrable, despite the efforts of artists and thinkers who have marvelled at the timeless force of the love story it relates. That mystery still disturbs us today.