Originally written for organ by the Beglian-American composer, Gaston Detheir, "Prelude sur le Dies Irae" is a meditation on the "Dies irae" motive from the Gregorian plainchant typically found in a Requiem mass. Marked "Andante tristamente" (moderately slow, sad), Dethier's setting is a hauntingly mournful yet serene and beautiful treatment of the traditional "Dies irae" theme.