In Spring 2014 the Vienna Musikverein became the setting for a very special encounter. The late Nikolaus Harnoncourt, who came to the world's attention as a period-practice doyen and arguably changed classical music more than any other artist after 1945, and Lang Lang, the superstar pianist of stunning virtuosity and natural musical instincts, embarked on their first and only collaboration on record. Together with the Vienna Philharmonic Orchestra, they produced a stunning recording of Mozart's Piano Concertos Nos. 17 and 24. This documentary is a revealing insight into the creative processes of two of the classical world's most distinctive voices.