In the fall of 1145, the younger son of Robert of Gloucester switches sides, abandoning his father and the cause of his aunt, the Empress Maud. Philip FitzRobert will not only fight on King Stephen's side, but he has turned over a chain of key garrisons, including the newly built castle at Faringdon, and its clever and unscrupulous castellan Brian de Soulis. Not all the men in that castle agree to changing sides in the eight-year fight for the crown of England between the King and his cousin the Empress. Thirty knights, unwilling to take part in what they see as treason, are taken as hostages by the King. One of their number, however, has disappeared, swallowed up without a trace. He is Olivier de Bretagne; and Brother Cadfae is prepared to sacrifice everything to find and free him. But Cadfael has few leads and the best one - de Soulis - has been stabbed to death by an unknown hand.