We follow Stefan Knüpfer, Steinway & Sons' Master Tuner in Vienna, as he works with some of the world's best-known concert pianists, including Pierre-Laurent Aimard, Lang Lang and Alfred Brendel.
With fascinating rehearsal and recording footage, the film reveals the art, the science and the passion behind the quest for sonic perfection, and how unsung hero Knüpfer is pivotal to realising the vision of each virtuoso.