This illuminated manuscript, a gradual of large size which the whole congregation of monks could see and read as they sang in choir (just as they are shown doing in an illustration in the manuscript itself), was previously unknown to scholars and has only recently come to light. It contains fine miniatures which can be attributed to Girolamo da Milano (died 1449), otherwise known as the 'Olivetan Master'. Indeed the manuscript sheds considerable light on the oeuvre and style of this master, otherwise a shadowy figure known chiefly for illuminations on detached leaves or cuttings. The book discusses the manuscript and its illuminations in the context of artistic developments in 15th century Lombardy. It is magnificently illustrated with a full colour reproduction of the gradual.