In 1789 Wolfgang Amadeus Mozart visits the grave of Johann Sebastian Bach in Leipzig, looking for a sign, a signal, an answer to an enigma that has haunted him since childhood: Was Bach murdered by a famous oculist? And years later, was Handel a victim of the same doctor?

Allegro follows his investigation, from the salons of London to the streets of Paris, recreating an enthralling and turbulent time, full of rogues and brilliant composers, charlatans and presumptuous nobles. Running parallel to this search is the rise of Mozart, his knowledge and fame, his trials and losses.