An old friend's promise of access to some rare texts of Aristotle's has taken Master William Falconer far from Oxford to the remote Furness Abbey. While crossing the dangerous shifting sands of Lancaster Bay, he witnesses the recovery of a body from the banks of the River Kent. It is only later that the full significance of this event is revealed.

Back at the abbey the body is identified as that of a monk who disappeared twenty years earlier. But his death may not have been an accident - the dead man was to have been the new abbot, and the present incumbent took his place exactly two decades ago.

Convinced of the abbot's innocence, Falconer's friend asks Master William to look into the matter. Falconer's investigations lead him further north, beyond the lakes and mountains of Furness Abbey to the fireside of a woman living at Kent's Bank. There he discovers a treachery long kept hidden...