The Tarnished Chalice by Susanna Gregory

In 1356, on a bitter winter evening, Matthew Bartholomew and Brother Michael arrive in Lincoln—Michael to accept an honor from the cathedral, and Bartholomew to look for the woman he wants to wed. It is not long before they learn that the friary in which they are staying is not the safe haven they imagine—one guest has already been murdered. It emerges that the dead man was holding the Hugh Chalice, a Lincoln relic with a curiously bloody history. Bartholomew and Michael are soon drawn into a web of murder, lies, and intrigue in a city where neither knows who can be trusted.