On a snowy December night in 1363, Brother Wulfstan ventures from the warmth of St. Mary's Abbey into the town. Worried by the decline in his patient, an unnamed pilgrim, he asks Nicholas Wilton, the Master Apothecary, for a herbal remedy. But the pilgrim dies in agony later that night. It is only when the same medicine proves fatal to another man - the ward of John Thoresby, Lord Chancellor of England - that suspicions are raised and Owen Archer, formerly Captain of Archers, is dispatched to York to discover the truth. As his cover he will work as the apprentice of Nicholas Wilton. However, Wilton is very ill and so it is from Wilton's beautiful, high-spirited and fascinating wife Lucie that Owen will learn the trade. As he unravels the complicated mystery, Owen is drawn into York life. But when there is another mysterious death, Owen must count Lucie among the suspects.