The Riddle of St. Leonard's - Candace Robb

Medieval York is wrapped in a dangerous riddle that only Owen Archer can unfurl. The fetid summer heat of 1369 has the citizens of York besieging Owen Archer's apothecary wife, Lucie, for physicks against noxious vapors. But more than pestilence is in the air. Owen is summoned to investigate the theft of rare treasures from St. Leonard's Hospital and the untimely deaths of aging patients. What links a brutal robbery, a fatal fire, a lay sister some still call whore, and a homeless urchin who shoots an arrow as straight as Owen himself? Country lore and town gossip lead him deep into the past, toward a killer with a heart blacker than the plague itself...