Henry of Grosmont, first Duke of Lancaster, cousin and friend of Edward III, was a soldier, statesman, and diplomat. His Book of Holy Medicines of 1354, an astonishing composition by a secular nobleman, is a classic of penitential thinking and intense spirituality that has never been available in a full translation. Catherine Batt's sensitive and profoundly informed translation into modern English brings to life the work's allegorical account of the wounds of sin and its meditative processes of healing. Her annotations and substantial introduction place the text within the political, literary, and discursive networks of later fourteenth-century England and its multilingual culture, and they open up important new literary connections in England and on the continent, where Lancaster spent much of his career. His Book is now accessible to modern English-speaking readers as a classic of medieval spirituality and lay writing alongside the works of Margery Kempe and Julian of Norwich.