Lothair, a wealthy young orphaned Scottish nobleman (loosely based on The 3rd Marquess of Bute) has been brought up in the legal guardianship of his Presbyterian uncle Lord Culloden and of a Catholic convert, Cardinal Grandison (based on Henry Edward Cardinal Manning). When he comes of age Lothair finds himself the centre of attention of three fascinating women, Lady Corisande, Clare Arundel, and Theodora Campion, representing the Church of England, the Roman Catholic Church, and the Radical cause respectively. Wavering in his allegiances, he unsuccessfully proposes marriage to Lady Corisande, almost joins the Catholic Church, and finally joins Theodora in Italy as a volunteer in the army of Garibaldi, which is fighting to take the Papal States for Italy. Theodora is killed at Viterbo, and Lothair is seriously wounded at the Battle of Mentana, but is nursed back to health by Clare Arundel, who tries to persuade him that he was saved by an apparition of the Virgin Mary. He takes refuge with the bohemian dandy Mr. Phoebus (a thinly disguised Frederic Leighton), who takes him to Syria, which, as the cradle of Christianity, seems the ideal place to reflect on the roots of the Christian faith. In Jerusalem he meets Paraclete, a mystic who teaches him that there is truth in many religions. Lothair returns to England and decides in favour of the Church of England, resisting the attempts of Cardinal Grandison and other prelates, including Mgr Catesby (modelled on Thomas Capel), to convert him to Catholicism. The novel ends with his marriage to Lady Corisande.