Narrated by the middle-aged artist and Second World War army Captain, Charles Ryder, Brideshead Revisited tells the story of his involvement with the Flyte family: Catholic aristocrats whose family seat is the splendid Brideshead Castle.

Having met Sebastian Flyte as a fellow student at Oxford University, middle-class Charles becomes his bosom friend, throwing himself wholeheartedly into the glamorous and decadent lifestyle of the young aristocrat and his exotic social circle. He is gradually introduced to the other members of Sebastian’s family: to Lady Marchmain, the pious matriarch; to Bridey, the awkward, ponderous elder son; to Sebastian’s beautiful sister, Julia, newly embarked on her first season as a debutante; to Cordelia, the deeply religious, but boisterous, younger sister; and to Lord Marchmain, estranged from his wife, and living a life of luxury with his mistress in Venice.

As Charles is drawn more and more deeply into this fascinating and troubled family,  he becomes increasingly aware of the tensions in their midst. Sebastian and Julia come to feel increasingly constrained by their Catholic faith (and by their mother’s strict adherence to that faith); Charles witnesses, and to some extent becomes complicit in, Sebastian’s gradual descent into alcoholism; Julia plans to marry the exciting, but somewhat shady, businessman and politician, Rex Mottram.  Charles's blissful time in Arcadia comes to an end as Sebastian turns away from him and Lady Marchmain accuses him of encouraging her son's addiction.

Expelled from Brideshead, Charles moves to Paris to study art, putting the Flyte family firmly behind him. From a distance he hears of Sebastian's continuing deterioration, and the problems Julia faces in marrying Rex.  He becomes briefly involved once more, when asked by Julia to go to Morocco and bring back Sebastian before Lady Marchmain dies.  Charles finds Sebastian sick and worn, but unwilling to leave Morocco and the German army deserter he has befriended.  On hearing of Lady Marchmain's death, Charles leaves Morocco without Sebastian, whom he will never see again.

Ten years have passed.  On the brink of the Second World War, Charles Ryder is married to the well-connected Celia, and has developed a career as a successful architectural painter. But when their paths cross again unexpectedly aboard an ocean liner, he falls in love with Julia Flyte.  Both decide to divorce their spouses, and they set up home together at Brideshead.

As Charles and Julia make plans to marry, anticipating the happiness and security which has so far eluded them, events take an unexpected turn when the terminally ill Lord Marchmain returns to Brideshead Castle to end his days in his ancestral home. Appalled by his elder son's choice of bride, he bequeaths Brideshead to Julia; if Charles marries her, he will inherit the great house he has so loved.  A lapsed Catholic convert, Lord Marchmain initially resists the attempts of the more devout members of the family to make him see a Catholic priest. However, in a moving deathbed scene, Lord Marchmain appears to embrace his faith again and he receives the last sacraments from the priest he had previously rejected. Charles Ryder, witnessing this scene, experiences a profound sense of its signficance, and we are led to believe that it marks his conversion to the Catholic faith. Julia, who has long been pondering the religious implications of her forthcoming marriage to Charles, is also deeply affected by the events at her father's deathbed, and she decides shortly afterwards that the marriage cannot go ahead.

The story ends where it began, with the middle-aged Charles Ryder billeted at Brideshead Castle, which has been requisitioned by the army. Entering the chapel attached to the house, he experiences a deep feeling of satisfaction as he sees that the sanctuary lamp is now re-lit: a symbol not only of his own newly-acquired Catholic faith, but also of its restoration to those members of the Flyte family who had temporarily lost touch with it.