Set in 15th-century England, the first in a series by Grace (a.k.a. P.C. Doherty) introduces Kathryn Swinbrooke, a physician and apothecary in Canterbury. Civil war has ended with the victory of the House of York, but the Archbishop, Alderman John Newington, and the town council are worried about a succession of poisoning murders of pilgrims on their way to the Shrine of St. Thomas Ö Becket. The elders engage Kathryn to work with soldier Colum Murtagh, newly appointed Special Commissioner to the city, to find the murderer. Kathryn quickly deduces that the villain is most likely a physician himself and that he's using Chaucer's Canterbury Tales to choose his victims. With Colum and her raunchy, devoted maid Thomasina in tow, Kathryn visits fetid slums and quiet churches, eventually ferreting out the murderer's secrets, even as she broods over her own. A weakly motivated plot and, except for Thomasina, characters who remain stubbornly unsubstantial are partly salvaged by the lively re-creation of time and place. Mildly interesting historical mystery--best enjoyed by fans of the genre.