Music lovers and readers the world over are familiar with the haunting account of the commissioning of Mozart’s Requiem in Otto Jahn’s biography: ‘A stranger, tall, thin, gravelooking, dressed from head to foot in grey… presented Mozart with an anonymous letter begging him to name his price for the composition of a Requiem…’ Mozart became convinced that the spectral caller was an emissary from the afterlife come to summon him away.

With a start like that, and the turn of events which followed, it is hardly surprising that the piece soon became entangled in a web of romance: suggestions that it was bound up with a plot against Mozart’s life still refuse to lie down. The story of the mysterious grey-clad stranger, though unforgettable, is based on a letter since exposed as a forgery. Nevertheless, while the now generally accepted truth of the matter is less sinister, it is hardly less bizarre: there was a certain Count Franz von Walsegg who was in the habit of commissioning works from established composers, then having them performed in his castle for his audience to guess the composers.

Mozart died before he could finish his Requiem. Faced with financial ruination, his widow, Constanze, sought desperately to have the work completed by someone else. The job fell to Franz Xaver Süssmayr, a pupil and friend with whom Mozart had discussed the progress of the Requiem in his final days and who had the ability to duplicate Mozart’s handwriting. The task that faced him was enormous: of the work’s eleven movements, only the Introit and Kyrie are mostly Mozart. Of the next eight sections the orchestration is mostly Süssmayr’s, following a few sparse indications of scoring in the composer’s sketches. Süssmayr’s remarkable salvage job was duly delivered to the Count in 1793.