While Sebastian and Charles are sunbathing atop the roof, Cordelia comes clamoring up. She’s eleven and talks about her pig, Francis Xavier.
Charles hears that Cordelia is a troublemaker at her Catholic school.
Despite Sebastian’s reprimands, Cordelia refers to Charles by first name instead of calling him "Mr. Ryder." She tells Charles that she’ll pray for him because he’s agnostic.
Cordelia tells Charles that she has six god-daughters in Africa which the nuns named after her for five schillings apiece.
At Brideshead over Easter, Cordelia spills the beans to Lady Marchmain about Sebastian being drunk alone in his room.
When Sebastian leaves to go to London, Cordelia tells Charles to give him "her special love."
Cordelia is with the rest of the family and Samgrass at Brideshead after Christmas. When they discuss art, Cordelia asks Charles to confirm that modern art is "bosh." He does.
After the hunting party, Cordelia comes back and reports that Sebastian has run to a hotel bar and gotten himself "in disgrace."
After Charles gets a stern talking-to by Lady Marchmain and leaves Brideshead, he gets a letter from Cordelia. She reports that she’s been supplying booze herself, that Rex and Julia are getting chummy (she disapproves), and that Samgrass has been found out and left. She adds that Rex is taking Sebastian to a doctor in Germany to try and do something about his alcoholism.
When Rex is converting to Catholicism, Cordelia tells him all sorts of humorous lies about the dogma. He buys most of it, and she calls him a "chump."
When Julia has her change-of-plans Protestant wedding, Cordelia is disappointed that she doesn’t get to be a bridesmaid. She begs Julia not to get married and then tells her that she hopes she will be "always happy."
When Lady Marchmain falls ill, Cordelia comes to London to take care of her in Marchmain House.
When Charles is commissioned to paint Marchmain House, Cordelia comes by to watch. He takes her out to dinner at the Ritz. She is fifteen but, in his opinion, not as beautiful as Julia.
Over dinner, they discuss Sebastian. Charles realizes that Cordelia knew more than he thought she did, and she professes that she loves her brother "more than anyone."
They discuss religion; she explains that Sebastian and Julia are tied to religion forever, and that no matter how far they wander from it, they will always be brought back by "a twitch upon the thread" that holds them.
She discusses her mother, explaining that people hated her when they wanted to hate God.
She hopes she has a vocation so she can be a nun.
Cordelia ends up a nurse in Spain.
While Julia and Charles are living together at Brideshead, Cordelia comes by for a visit. She’s 27 now. Julia says that she’s grown up "quite plain," but Charles goes so far as to think her ugly when she arrives.
When he watches Cordelia talk with her Nanny, however, he realizes she does have a beauty of her own.
Cordelia updates Charles on Sebastian. She explains that she traveled to Tunis to find him and speak with The Superior.
She explains that Sebastian is actually very holy. She believes that she and he are similar because they don’t fit in to the real world, but they don’t fit into the monastic world either.
As Cordelia imagines Sebastian living his life out trying to be holy and falling back into drinking every now and then, she isn’t worried. She thinks this isn’t such a bad way of living, and adds that "no one is ever holy without suffering."
Cordelia asks if Charles thought she was "thwarted" when he saw her for the first time after so many years. He says yes, and she responds that she thought the same thing about him and Julia.
Cordelia stays at Brideshead with the rest of the family when her father comes there to die. He asks her to sit with him while he falls asleep, and she concludes that he is afraid of the dark.
She sides with Bridey, adamantly insisting that her father gets a priest to perform the Last Rites.
Cordelia is ultimately out of town on the night her father passes away.
When Charles speaks with Nanny Hawkins in the epilogue, she tells him that Cordelia is abroad with Julia, helping with the war effort.