Morality Play by Barry Unsworth

From the publisher:
In the late fourteenth century, the country stricken with plague, famine and the consequences of war with France, a priest joins a group of impoverished travelling players as they take the body of their dear friend to the nearest town for burial. To pay the burial fees they decide to put on a play. On hearing that a young woman is to be hanged for the murder of a twelve-year-old boy, the company leader, Martin, desperate to augment their depleted funds, persuades the players to re-enact the murder. But as the players investigate the circumstances of the boy's death, doubt is thrown on the young woman's guilt. Over the two days that they perform their play, digging deeper into the murky circumstances that surround the murder, they come close to revealing a shocking truth that puts them all in mortal danger.