Wolfgang Amadeus Mozart was at the height of his popularity in Vienna when he composed his Piano Concerto No. 20. So why is this piece—one of his two piano concertos written in a minor key—so turbulent? Hilan Warshaw takes us on a tour of this dramatic work, along with a sneak peek of its performance by the ASO and special guest Jonathan Biss, under the baton of Sir Donald Runnicles.