Holmes meets Joseph Haydn in London and the two form an instant bond.
This encounter and a later one with Haydn's young acquaintance, Beethoven, assume a new importance when Holmes and Watson travel to Vienna on a diplomatic mission and are consulted by Constanze Mozart, widow of Wolfgang Amadeus Mozart.
Who commissioned her husband to write a requiem? Why was the commission made through an intermediary? And how can the commissioner be persuaded to pay the balance of the fee when the Requiem remains unfinished?
Holmes applies the full panoply of his skills to deliver a solution critical to the history of music.