The year 1264 marks a turbulent period for England, with Simon de Montfort challenging the sovereignty of King Henry III, the Crown at the point of expelling all Jews from England, and Roger Bacon's scientific experimentalism contending against faith and superstition. Bacon's pupil at Oxford, Regent Master William Falconer, finds his belief in Aristotelian logic (though not his conviction that the earth is round) sorely tested by a series of murders beginning with Margaret Gebetz, servant to his surly fellow master John Fyssh. The young woman's throat was cut practically within sight of Thomas Symon, who has arrived at Oxford to study with Falconer; but the only clue to her murder is a mysterious book she was carrying even though she was illiterate. The book makes its way from the hands of Gebetz's Jewish friend Hannah to Symon to rhetoric master Richard Bonham, who peremptorily confiscates it, to Fyssh, who's seen with it shortly before his own murder. First-novelist Morson drops teasing clues concerning the book's true nature, though it's only the most dedicated medieval historian who'll beat Falconer in tying the killer to the background political conflicts. Conscientiously shadowy--the Dark Ages at their darkest-- with a whirlwind climax: a between-courses palate-cleanser for Ellis Peters fans.