An extraordinary new production of Wagner's Tristan und Isolde opens in Paris this week, promising to deliver fresh insight into Wagner's operatic masterpiece. Tom Service talks to director Peter Sellars, conductor Esa-Pekka Salonen and video artist Bill Viola. Meanwhile in London, a new play, Tristan and Yseult, opens at the National Theatre. Psychologists and philosophers explain why the Tristan myth has endured so strongly since the Middle Ages and is still relevant today. And leading musicians talk about their make-or-break career decisions.