The story opens in the summer of 1266 in the Basilicata, where Gregorio Villani, Grand Master of the Knights Hospitallers, lies dying of a fever. Tormented by the sin of his illicit union and the terror of damnation, he summons his son Francesco from the court of Avellino. The elder Villani demands a terrible sacrifice: Francesco must renounce his courtly life and the woman he loves, Ilaria Caselli, to enter the Benedictine monastery of Monte Cassino and atone for his father's soul. Despite his initial revulsion and despair, Francesco yields to his father's dying command, promising to become a monk.
Francesco returns briefly to Avellino to bid farewell to his former life. He is torn between his allegiance to the Ghibelline cause, the impending descent of Conradino of Swabia, and the desperate love he holds for Ilaria. During a magical night-time masque, he meets Ilaria, but his inability to explain his sudden departure or his father's decree drives a wedge between them. Ilaria, wounded and proud, recoils from his sacrifice, and the two part ways in bitter misunderstanding. Francesco takes the monastic vows at Monte Cassino, but finds only loneliness and spiritual emptiness among the monks.
Time passes, and the political landscape of Italy shifts as Conradino marches southward to claim his heritage. Francesco is summoned to Rome by Pope Clement IV, drawing him back into the turbulent world of political intrigue and factional strife. In Rome, he encounters Ilaria once again, now married to the powerful Ghibelline nobleman Raniero Frangipani. The meeting deepens Francesco's internal agony, as he witnesses the woman he loves bound to his bitterest enemy.
Sent on a mission to Naples by the Pontiff, Francesco wanders through a war-ravaged landscape filled with mercenaries, outlaws, and rival armies. He encounters colorful figures such as the free-lance leader Rupert of Teck and experiences strange adventures in the remote reaches of the Campagna. Throughout his journey, he struggles with the conflict between his vows and his unquenched passion for the world and for Ilaria. The novel explores the heavy price of obedience, the pain of unrequited devotion, and the dark inevitability of fate as the tragedy of the Hohenstauffen dynasty unfolds across Italy.
