Bloodstone (Brother Athelstan 11)

"December, 1380. When the corpse of Sir Robert Kilverby, a wealthy Cheapside merchant is discovered in a locked room, Brother Athelstan accompanies the King's coroner to investigate. For the late Sir Robert had in his possession a priceless relic, a sacred bloodstone which he was planning to donate to the Abbey of St Fulcher-on-Thames. The bloodstone has disappeared and the Regent, John of Gaunt, who covets the relic for himself, is taking an uncomfortably close interest in the case."