Anthony provides Charles with the back story on Lord Marchmain. She is a strict Catholic and Lord Marchmain converted in order to marry her. When he wanted a divorce, she refused on account of her religion. They are now separated and he lives in Venice with his mistress, Cara. He left his wife with everything – both Brideshead and Marchmain House and all the servants who went with them.
Towards the end of their first summer together, Charles and Sebastian go to Venice to visit Lord Marchmain and Cara. Charles is surprised at how young Lord Marchmain appears and repeatedly calls him "Byronic."
Charles gets more info from Cara. She says that Lord Marchmain’s first love was Lady Marchmain, but that now he hates her and everyone who knows her. He can’t even completely love Sebastian because he is Lady Marchmain’s child. She claims this all stems from loving a woman before he was grown-up enough to do so.
After Sebastian leaves Brideshead in a huff, Lady Marchmain takes Charles aside. She is concerned about her son’s depression, and explains that Lord Marchmain used to drink this same way – both men were ashamed of being unhappy.
When Rex can’t get Lady Marchmain’s consent to marry Julia, he gets permission from Lord Marchmain instead. When Rex needs a Protestant ceremony instead of a Catholic one, Lord Marchmain again gives his consent.
When Lord Marchmain is ill and dying, he decides to live out his final days at Brideshead. Charles is at first surprised by his new somewhat caustic attitude, but realizes that dying slowly has a profound effect on one’s attitude.
Lord Marchmain explains to Julia and Charles that he met and hates Beryl, Brideshead’s new wife. He tells them he wants to leave Brideshead estate to the two of them, rather than to his eldest son.
As Lord Marchmain lives out his final few months, he never wants to be alone, especially in the dark. He insists that at least one member of his family is around at all times.
The doctor attending to Lord Marchmain explains to Charles that the man is afraid of dying.
Julia, Bridey, Cordelia, Cara, Charles, and the doctor discuss whether or not Lord Marchmain should have a priest perform the Last Rites before his death. The first time they bring the priest in, Lord Marchmain refuses to see him. The second time, when he is very close to death and in fact barely conscious, Lord Marchmain does not protest (perhaps because he can’t) and even gives a small sign of the cross.
Lord Marchmain dies, leaving Brideshead to Julia in his will.