The year is 1303, and the Benedictine monks of the abbey of St. Martin's-in-the-Marsh are accustomed to a comfortable existence within their sprawling, peaceful estate. But that begins to change when Abbot Stephen, a well-respected leader and a personal friend of King Edward I, is found brutally murdered in his chamber-with the door and windows locked from the inside. Soon Sir Hugh Corbett, Keeper of the King's Seal, arrives with his two henchmen to investigate.
Rumors about the ghost of robber baron Sir Geoffrey Mandeville riding through the Lincolnshire fens with a retinue of ghastly horsemen have been circulating by way of explanation; Mandeville's ghost is also thought to be responsible for the corpse candles glowing in the dark, supposedly forewarning men of their own deaths. But Corbett disregards the tales, suspecting that someone much closer to home is responsible for the bloody acts. As the mysterious death toll mounts, Corbett sets about unearthing the dark secrets that the abbey and its inhabitants have been hiding for far too long.