Oxford University, 1271: for the first time in the university's history a college is to be purpose-built. As old buildings are pulled down, a body is revealed. Only the skeleton remains but the skull is missing -- it is clear the man has been murdered. Regent Master William Falconer is distracted from his latest investigation -- examining the suicide of a serving girl -- and deduces that the body was hidden 20 years ago. He must rack his brains to recall significant events in Oxford during that decade, when England was involved in an earlier Crusade and the apparent ritual murder of a child shocked the community. Could this provide a solution to the case? As the heavens open, and Oxford is threatened with flooding, Falconer is drawn into violent events where the past and the present collide with startling consequences.