A learned Franciscan friar and his young novice companion arrive at a remote medieval abbey where a series of mysterious deaths among the monks demands investigation. As the friar applies his sharp intellect and powers of observation to uncover the truth, he becomes entangled in a web of forbidden knowledge, religious fanaticism, and institutional corruption. The search for a killer leads deep into the abbey's labyrinthine library, where dangerous secrets have been jealously guarded for generations.