As Proms 2013 gears up for its final week of concerts, Katie Derham presents the last episode of Proms Extra. Featured highlights include the sparkling John Wilson Orchestra and Wagner's epic love story Tristan and Isolde with the BBC Symphony Orchestra. David Owen Norris unlocks the secrets of music's most famous chord, the 'Tristan Chord', and Katie is joined in the studio by conductor Simone Young, violinist Janine Jansen and jazz pianist and composer Julian Joseph.