The film opens during World War II with shots of a British Army unit setting up a camp of some sort. Charles Ryder, a captain (Matthew Goode), introduces himself in voiceover. He tells us about how he's known many emotions, and he feels he's borrowed most of them from the family he was once involved with, but one emotion is fully his own: guilt.
Quick flashback to pre-war times, with Charles having a full beard shaved off in a barbershop, and mentioning that he's been painting in the jungle. Then we cut to an ocean liner during a storm. Some of Charles's jungle paintings are being shown to a crowd of passengers. Charles's wife Celia reads aloud from a glowing review of the paintings. Despite this, Charles looks unhappy. Celia tells him to "make an effort." He goes off and smokes in a corner. Suddenly he sees a beautiful woman -- Julia (Hayley Atwell) -- enter, look around, and leave. He runs out and pursues her through the ship, till she finally stops in a corridor, turns to face him, and says, "Hello, Charles."
Screen: "Ten years earlier"
A young Charles is packing to leave for Oxford. He goes to say goodbye to his father (a very funny Patrick Malahide), who doesn't seem to care very much that he's going. At Oxford, his pompous cousin Jasper shows him around and gives him advice on clothes and manners. As they cross the river, they see Anthony Blanche (Joseph Beattie) horsing around in a boat below, while Sebastian Flyte (Ben Whishaw) lounges in the same boat holding a teddy bear. Jasper says, "Sodomites, all of them. Steer well clear." When they reach Charles's rooms, Jasper says he should change them because they're in the front and he'll be bothered with people always in and out. Just then a drunk Sebastian comes up to the window and vomits into the room.
Later, Charles is cleaning up the mess when a servant comes in with flowers and a note from Sebastian, who is "contrite" and asks him over. In his room, Sebastian -- with the bear, called Aloysius, on a chair -- is peeling plover's eggs that his mother sent from their home, Brideshead, and offers Charles one. They talk a little. Charles tells him about wanting to be a painter. Sebastian doesn't know what he wants, except to be happy if he can. Later, more of Charles's friends come in, and make fun of Charles's humble background and artistic ambitions, but Sebastian stands up for him. One of the friends is Anthony Blanche, who kisses Sebastian on the mouth.
Charles and Sebastian are shown biking together and later boating and picnicking with wine and strawberries. Then Sebastian drives Charles to Brideshead to meet his old nanny. He says his family are all away. Charles is awed by the beautiful house and all the artwork inside. Nanny Hawkins welcomes them in her room and mentions that Sebastian's mother is coming. Sebastian immediately becomes ill at ease and wants to get away. As they're going out, Nanny Hawkins drops her rosary and Charles picks it up for her. Nanny mentions that she prays for Sebastian every day.
At Charles's insistence, they stay and look at the house and art a little longer, including the chapel. Sebastian dips his fingers in the holy water, makes the sign of the cross, and genuflects. Charles copies him. Sebastian tells him not to do it because he (Charles) isn't a Catholic. Sebastian becomes desperate to get away before his mother comes. They pass her car on their way out, and see a young woman inside the car, whom Sebastian says is his sister Julia. Charles asks more about them, but Sebastian is irritable and finally says, "I'm not having you mixed up with my family." Charles says he doesn't have any family himself, and Sebastian says Charles has him. Sebastian puts an arm around him and declares, "Sebastian and Charles contra mundum [against the world]."
At the end of term, Charles goes home, where his father greets him, "Back already?" One day while they're playing chess, a telegram comes saying Sebastian is injured. Charles takes the train to Brideshead, and Julia picks him up at the station. She tells him Sebastian hurt his foot playing croquet and it's not serious. But at the house, Sebastian is in a wheelchair and full of self-pity. The three of them go off to a little garden house, with Sebastian carrying a Victrola on his lap and servants accompanying them with wine. They eat apples and talk about religion and family. Charles says he's an atheist, and that his mother died while working for the Red Cross. Julia warns him that her mother takes religion so seriously that the local priest calls her a "living saint." She says she and Sebastian are heathens, but Sebastian corrects her, "I'm not a heathen, I'm a sinner." After Julia goes back to the house (knocking Sebastian's bear to the ground), Sebastian jokingly toasts with the wine, "Drink in remembrance of me."
There's a montage of Sebastian and Charles running around the gardens, having fun, and drinking. One evening they sit outside with a huge number of bottles and take turns making up fancy descriptions as they taste the different wines. Suddenly Sebastian kisses Charles on the mouth. They both go very quiet and look awkward. One day after that when they're skinny-dipping in a huge fountain, they see Sebastian's mother, Lady Marchmain (Emma Thompson) pull up to the house. Sebastian's brother Bridey (Ed Stoppard) and youngest sister Cordelia (Felicity Jones) are with her. As the boys are drying off behind a hedge, Julia comes up behind them to tell them that their mother is home and has asked Charles to dinner. In the house, Charles is walking down the hall when he sees Lady Marchmain in a room with her hand on Sebastian's shoulder, quietly saying, "We must all pray for God's forgiveness." Sebastian is crying. Julia comes up behind Sebastian and steers him to the dining room, saying, "He and Mummy often have these talks."
At dinner, we see that Lady Marchmain is intimidating and likes to play little psychological head-games with people. Sebastian says he and Julia have been invited to Venice to visit their father. Sebastian gets sulky as Charles warms up to his mother. When the topic of religion comes up, Sebastian announces that Charles is an atheist. Lady Marchmain nonetheless invites him to the chapel with the family after dinner. While there, Charles watches from the background as the family pray the Lord's Prayer and sing a hymn. Afterward, Lady Marchmain suggests to Charles that he go with the others to Venice. She wants him to look after Sebastian. She also remarks, "We must all accept God's limits, atheist or no."
In Venice, the three of them take a boat to where Lord Marchmain (Michael Gambon) lives with his mistress, Cara (Greta Scacchi). The couple greet them all affectionately. However, Julia confides to Charles later that she thinks their father likes Sebastian best. Over drinks, they all talk about art and Lord Marchmain says he doesn't like to go look at the art in Italy because it's too religious. Julia is a bit sharp with him over walking away from her mother. Lord Marchmain says to Charles, "A family of monsters, are we not?" He also mentions to Charles all the temptations to be had in Venice, while putting an arm around each of his children (the well-known shot from the trailer).
While Sebastian and Julia and their father are on the beach, Charles paints and talks with Cara nearby. She says that Lord Marchmain is "fragile inside" and "that woman nearly suffocated him." She points out that Lady Marchmain has warped her children as well, and says, "Her God has done that to her." Charles says he thought Cara was Catholic too. She says she is but "it's different in Italy. We do what the heart tell us and then we go to confession." She warns him about his "romantic friendship" with Sebastian, saying it might be just a phase for Charles but it's more than that for Sebastian. Then Sebastian and Julia run up and drag Charles off to play in the water with them. That night, Charles watches Julia from his window and starts putting the moves on her when she comes into the house, but she rebuffs him. A tipsy Sebastian comes in and takes Charles off with him as Julia shuts her door.
One night they all to a big party. There's such a huge crowd that they all get separated. Charles and Julia meet up outside and he kisses her, as Sebastian watches from a distance. She gets upset and runs away. He catches her and they kiss even more passionately, and then she runs off again. Charles sees Sebastian looking stricken, but goes after Julia anyway. We see a small chapel where Cara is kneeling in prayer as Lord Marchmain watches. Julia enters and kneels beside her. Charles comes in and watches. Sebastian enters and remarks, "Funny old religion, isn't it?" Charles tries to apologize to him but can't quite come up with the right words. Sebastian stops him with a finger on his lips and then goes off.
After a brief interlude at home, where Charles's father asks courteously if his friend died of his injuries, Charles is back at Oxford. He sees Sebastian staggering around drunk and goes to help him. Sebastian is trying to get away from a man called Mr. Samgrass whom his mother hired to keep an eye on him. He mentions that his mother is at Oxford and wants to see Charles. He says he himself isn't sure he wants to see Charles anymore. In a college dining hall, Charles meets Lady Marchmain, who's worried about Sebastian's drinking. She also warns Charles away from Julia because Julia has to marry a fellow Catholic. She asks Charles what he thinks his purpose in life is since he doesn't have any faith, and he says it's just to live his life and be happy. Despite not wanting him with Julia, she invites him to Julia's twenty-first birthday ball at Brideshead.
At Brideshead, Charles meets a visitor called Rex Mottram (Jonathan Cake) with a tortoise with diamonds in its shell, which he's giving to the family as a gift. Sebastian and Charles talk as Sebastian finishes bathing and starts to dress. Charles is trying to convince Sebastian that he's on his side, not his mother's. Sebastian is going hunting with some of his family, but plans to elude them and go somewhere to drink. But he doesn't have any money, and asks Charles for some. Charles is hesitant. We cut abruptly to the next scene, where Julia has just finished dressing, and she and Charles see each other through an open doorway. Then he sees her mother with her, so doesn't say anything.
At the ball, Lady Marchmain announces Julia's engagement to Rex. Rex and Julia dance, and Cordelia drags Charles onto the dance floor. Then they change partners. Julia confesses that she thinks about Charles's kisses all the time, but has no choice. A very drunk Sebastian comes in and tries to console Charles, but then turns belligerent. He shouts that he hates all of them, and that all Charles ever wanted was to sleep with his sister, and goes out. Lady Marchmain confronts Charles, who admits that he gave Sebastian money to go drinking, but accuses her of being the reason he drinks. They fight and she tells him to leave, which he does.
Screen: "Four years later"
Charles is preparing for his first London exhibition. Celia Mulcaster, his future wife, comes by as he's putting up the paintings, introduces herself, and comes on to him strongly. Back at his house, Charles finds Lady Marchmain visiting. She looks unwell and nearly collapses during the conversation. She says Sebastian has run off to Morocco and asks Charles to go bring him home, since he liked Charles best of anyone. She says, "All I ever wanted was to see them safe, and all they do is hate me." As she leaves, Charles catches a glimpse of Julia in the car.
Charles finds Sebastian's house in Morocco. A man called Kurt tells him Sebastian is in the hospital, and asks him to remind Sebastian that he (Kurt) is waiting for him. At the hospital, which is Catholic, the doctor says Sebastian has grippe and is very weak from that and alcoholism. A monk takes Charles to where an emaciated Sebastian is sitting outside. Sebastian can't travel, and doesn't want to anyway, even though Charles says he thinks Lady Marchmain is dying. Charles apologizes for everything, but Sebastian says, "I asked too much of you. Only God can give you that sort of love." He says he's happy where he is and that it's nice to have someone (Kurt) to look after. Back at Brideshead, Charles simply says to Lady Marchmain, "I'm sorry," and leaves.
We're back on the ocean liner again, with Charles and Julia. They go to her stateroom and make small talk for about a minute before the clothes start coming off. Afterwards, Julia mentions that her mother died without ever seeing Sebastian again. They get dressed and go up on deck, both in a giddy mood, and when Charles asks what happened to Rex, Julia teases, "I drowned him." Then they go down to a nearly-empty lounge for a drink and some talking and dancing. They talk about running away together. Charles wants to go to Brideshead, but Julia doesn't want to. For one thing, Rex is there. Charles promises to settle him.
At a London showing of Charles's jungle paintings, Charles again looks unhappy and Celia again tells him to "make an effort." Anthony Blanche shows up and mentions to Charles that everyone's talking about Charles's affair with Julia. He hints that Charles is hunting down members of the Flyte family out of "hunger." At Brideshead, Rex has the house filled with political visitors. Julia wants to get out, but Charles wants to settle things first. In the dining room, Bridey announces to the two of them that he's engaged. He calmly says that he won't bring his fiancee to visit because she's Catholic and would be offended by Julia's "living in sin" with Charles. Julia runs out. Charles scolds Bridey and follows. In the hall, he hugs Julia and tells her to take no notice of Bridey.
In the library, while Julia waits outside, Charles and Rex talk. Rex mentions that he wasn't Catholic to begin with and just converted to marry Julia, and says that Charles should have done the same if he wanted her so badly. He doesn't love Julia, and though he thinks Charles really just wants the house, he offers to divorce her if Charles will give him a couple of his paintings, which are worth a lot of money. Charles agrees. They hear Julia walk away. Charles finds her outside by the fountain, where she's in shock from what she overheard. She blurts out that she's always tried to be good but she was never good enough, and God keeps punishing her. She thought she could be free with Charles, but she still hears voices saying she's a "bad little girl living in sin."
Julia and Charles are leaving when they see Lord Marchmain and Cara arrive, and turn back. Lord Marchmain is ill and has come home to die. Julia tells Bridey to get a priest. Charles informs Lord Marchmain of this. Lord Marchmain doesn't see why Charles should care. He's feeling guilty about having let his family down, but when the priest does come, Lord Marchmain yells at him to get out. As the family talks outside (Cordelia mentions that Sebastian is working for the monks at the hospital in Morocco and seems to be content there, and it's "a sort of salvation"), Julia gets increasingly upset with Charles's interference about the priest. Later they fight over how he "bought" her from Rex. She accuses him of just wanting the house. He confesses that from the first time he saw it, he would have done anything to be "part of that dream," but says he'll leave with her after everything is over. Early in the morning, Lord Marchmain gets worse and the priest is sent for again. Charles watches as the family and Cara kneel around the bedside and the priest gives absolution, telling Lord Marchmain to give a sign if he repents of his sins. Lord Marchmain makes the sign of the cross before he dies. Julia looks relieved and smiles up at Charles. He looks disturbed and goes out.
Julia comes to him and he confesses, "I wanted too much." She says it's no one's fault, but she can't be with him. She explains, "I can't shut myself off from His mercy." Charles says he hopes her heart breaks, but he understands.
We're back at the Army camp, which is being set up at Brideshead. Charles reflects, "Did I want too much? Did my own hunger blind me to the ties that held them to their faith?" He says that now he's "alone enough to see the light." He talks with a soldier named Hooper, who fills him in on the family that lived there (not knowing of Charles's connection with them). Julia has been living there, but has gone overseas with the Women's Service. Her older brother, presumably Bridey, was killed in the blitz. Hooper, who isn't religious, isn't impressed by the family's faith or traditions and says, "The future belongs to us, as long as we don't get shot."
Charles goes into the chapel alone and dips his fingers in the holy water. He approaches a burning candle. We see images of Sebastian and Julia going through his mind. He moves to put the candle out, hesitates, stares at it, then turns and walks out.
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