1842: Orry Main leaves the cotton plantation near Charleston that he's heir to on his way to West Point for two years of officer's training. On the way, he meets and falls in love with Madeline Fabray, who agrees to write to him. However, her father needs her to wed Orry's rude neighbor, rich plantation owner Justin LaMotte. Orry's letters to Madeline become intercepted by her father so she becomes susceptible to Justin's generous courting. At West Point, Orry meets fellow cadet George Hazard, son of a Pennsylvania manufacturer. The hazing lives up to its reputation, not least due to drill master Elkanah Bent, who takes particular pleasure in humbling the cadets at sword-practice, but is humiliatingly defeated by Orry. George introduces Orry to his Pennsylvania family and their iron factory. After graduating and returning home, Orry stops an overseer from happily whipping a slave, but his father, Tillet, refuses to sack the sadist.
George distracts Orry, whose brooding about Madeline wrecks his West Point performance. Bent bluffs his way out of a court-martial but its president eventually bullies him out of West Point. At a party hosted by Tillet Main, Justin scolds Madeline for disagreeing with separatism and arranges for a slave to give public offense so the overseer is allowed to punish him with branding. Bent trades on his status as the bastard son of Ohio's U.S. Senator to get commissioned as an infantry captain in the Mexican-American War. In command once again of lieutenants Orry and George, he sends them on a suicide mission. Both survive but Orry is crippled for life. Constance, the daughter of the colonel who saves Orry from dying from his wounds, becomes George's true love. When George's father dies, he resigns his commission and returns home. The branded slave runs away and even reclusive Orry joins the manhunt, reuniting him with reluctant Madeline and starting their secret affair.
George and Orry's friendship is severely tested when one of the Mains' slaves escapes. Orry still travels to Pennsylvania for George and Constance's wedding, but when he hears a speech given by Virgilia Hazard at an abolitionist rally, he realizes the depth of their divisions. George's mother decides that he should assume full control at the family iron works, much to his older brother Stanley's dismay. Orry's father dies, and his first act as owner of the plantation is to fire the cruel slave overseer. Orry's cousin Charles finds himself challenged to a duel and Orry acts as his second. Orry's sister Ashton is something of a flirt and being pursued by lawyer James Huntoon. The Mains visit the Hazards for the summer, where Charles and George's younger brother Billy, who are both West Point-bound, become close friends. Orry's younger sister, Brett, takes an interest in Billy but he seems to prefer Ashton. Madeline's marriage to Justin continues to decline after he beats and whips her.
When the Hazards visit Mont Royal, Billy loses interest in Ashton when he sees her with another man, turning his interests to Brett. Virgilia meets James Hontoon's coachman Grady and forms an instant attraction to him. After spending the night together, she helps him run away to the North, which leads to a confrontation with Huntoon. Orry feels he has little choice but to ask the Hazards to leave. Virgilia and Grady are soon living together as husband and wife but that makes even some of the most ardent supporters of abolition uncomfortable. Billy and Charles graduate from West Point with Billy assigned to go to Washington, D.C. and Charles sent to Texas under the command of Robert E. Lee. Billy proposes to Brett, but Orry will not allow him to court her. Ashton continues to scheme her way through society and turns to Madeline when she gets into trouble. Meanwhile, Madeline's father is on his deathbed and shocks her by revealing a hidden family secret.
With Madeline locked in her room and nearly starving to death, Justin convinces the doctor to prescribes a daily dose of laudanum despite its addictive qualities. Madeline is soon a very different woman: submissive and with few words to say, having little memory of her love affair with Orry and their decision to run off together. Orry and Brett travel to Philadelphia where he wants to give his good friend George Hazard his share of the profits from their joint cotton mill. Unfortunately while there, Virgilia has a confrontation with Orry over slavery. Orry and Brett leave and it will be some time before before he and George see one another. On the trip home, they are stopped by a group led by abolitionist John Brown. Ashton, now married to James Hontoon, still spends a good deal of her time in bed with her other lovers. The secession movement quickly gains ground and war is seen as inevitable should Abraham Lincoln win the forthcoming elections.
Lincoln is elected President, and George pays a surprise visit to Orry to apologize for what his fanatical sister said on their last visit and they resolve their differences, with Orry finally consenting to Brett marrying Billy. Ashton is still out for revenge and arranges for Billy to be attacked on the street, though it's not successful. She then turns to her lover Forbes LaMotte, Justin's nephew, to get the deed done, and Billy and Brett's wedding seems to be just the right day. Madeline overhears the plot and rushes to tell Orry, who tells her she will stay at Mont Royal and never return to Justin. Bent plots to run any blockade imposed on Southern ports. Orry travels to Pennsylvania to finish repaying George his investment in the cotton mill and realizes the full extent of the hatred that now exists. Confederate forces attack Fort Sumter and war is declared, forcing George and Orry say farewell, not knowing what the future may hold for their families or their friendship.
