On her wedding night, Kate Judson Lawrence, the granddaughter of an Irish servant, learns that her wealthy, Philadelphia Main Line society husband, Bill, is impotent. After Bill flees from their hotel room, Kate seeks comfort from childhood friend Mike Flanagan, a second-generation Irish laborer, and the next day, learns that Bill died in an automobile accident. When Kate gives birth to Anthony Judson Lawrence, Bill's martinet mother, guessing the child is not Bill's, threatens to disown the baby. Uninterested in the Lawrence fortune, but determined to climb Philadelphia's social ladder, Kate threatens to make public what happened on their wedding night and taint the Lawrences' reputation, unless Tony is allowed to keep the Lawrence name. Despite Mike's coarse appearance, he is determined to get rich and marry Kate. Instead, Kate chooses to live a life of genteel poverty, saying that Mike can never "open the right doors" for Tony. Twenty years later, Tony is studying pre-law at Princeton University and working summers at Mike's successful construction company, when he has a chance encounter with Joan, daughter of attorney Gilbert Dickinson. Although not engaged, she is "expected" to marry Carter Henry, but sees folly in the arranged marriages of her social class. Although Tony can afford no more than "hamburger and chili," she dates him, falls in love and becomes troubled that Tony's pride and her family's prejudice will delay their marriage for years until he is settled into his profession. Heavy-drinking Chester "Chet" Gwynne, Tony's Princeton buddy and distant relation to Joan, is the bitter victim of a manipulative family, who have tried to marry him off against his will and who control his fortune through his guardian and uncle, Morton Stearnes, who works with Dickinson. Chet advises Joan to get pregnant to force the marriage and warns her not to let the family "buy off" Tony. When Joan later attempts to seduce him, Tony, unwilling to take advantage of her, instead agrees to elope, but before they leave, Gilbert intervenes and offers to mentor Tony through law school by giving him a job at his firm, if he waits to marry Joan until he graduates, asserting that Tony will then be in a more advantageous position from which to support Joan. Then, Gilbert slyly convinces Joan that Tony placed his ambitions ahead of his love for her. Disappointed in Tony, Joan travels to Europe and finds Carter, unaware that Gilbert arranged to reunite them. Weeks later, when Tony learns that Joan and Carter have married, he assumes that she gave herself to "the highest bidder." After a drunken binge from which he is rescued by Chet and Mike, Tony becomes more competitive and manipulative. When he learns that fellow student Louis Donetti, a second generation Italian, is vying for a summer job, living on an estate and helping the older, esteemed attorney John Marshall Wharton write a book, Tony maneuvers to get the job for himself. Thus, he is able to break off with the Dickinson firm, while widening his sphere of future connections. His intelligence and hard work is appreciated by Wharton, and Wharton's wife Carol, who is older than Tony but much younger than her husband, becomes attracted to him. When she comes to his bed one night, Tony, not wanting to offend her with rejection, nor alienate himself from Wharton and thwart his ambitions, begs her to divorce Wharton and marry him. As he has planned, Carol is unwilling to "start over," but nevertheless flattered by his offer, and Tony maintains the good opinion of both husband and wife. Soon after, Wharton offers him a job at the firm and Tony decides to specialize in tax law, a growing subfield of the profession, but the Korean War disrupts his plans. Tony is drafted into a non-combat commission, but Chet loses an arm in a battle and Carter, who joined to escape his unhappy marriage, is killed. After the war, Tony takes his place as the lowest junior partner of Wharton's firm. The successful Louie, who now represents unions and holds no grudge against Tony, meets by happenstance Mrs. J. Arthur Allen, the eccentric, but kind and shrewd, widow of a millionaire oilman, and sends her to Tony's office to make a will for her dog. Knowing that Mrs. Allen, who is Joan's aunt, is a key client at Dickinson's firm, Tony develops a proposal that will save her $200,000 a year in taxes, using information from the county clerk that was secretly acquired through Mike's connections. Throughout his presentation to Mrs. Allen, Tony carefully avoids any behavior that can be construed as stealing another firm's client, as it would cost him his career. Mrs. Allen and Joan, whose opinion she trusts, approve of his plan, forcing Morton to turn over her affairs to Wharton's office without censuring him. Tony moves up to senior partner at Wharton's firm, and Joan noncommittally agrees to date him again, although she still believes he is driven only by ambition. At a dinner party with Joan, Tony witnesses a disagreement between Dr. Shippen "Ship" Stearnes, a relative of Chet who, as executor of the Lawrence estate, knows about Tony's illegitimacy, and Morton, who leaves the party early in anger. When Morton is murdered later that night, a drunken Chet, who is being held for the murder, calls Tony from the city jail. Chet admits to visiting Morton that night, but claims Morton was alive when he left in an angry mood. Although Tony is not a trial lawyer, Chet wants him to represent his case. Ship, too, pressures Tony to take the case, to assure that the presumably guilty Chet is institutionalized with little publicity or scandal for the family. Joan, who is loyal to Chet, believes the family will sacrifice him to assure that their mistreatment of him does not become public. Fearing that Tony will either "sell out over the long run" or lose status, she offers to pay for an out-of-town attorney, who is free of Main Line influence, to represent Chet. When Tony vows to investigate fully the murder and free Chet, Ship threatens Kate that he will publicly reveal Tony's real father, forcing Mike and Kate to tell Tony the truth about his past. Mike explains that he and Tony could weather society's disapproval, but Kate's reputation would be ruined irreparably. Mike fears there is no way to protect Chet without hurting his family, but Tony, though worried about his mother, feels it is his duty to help Chet. Louis is the prosecutor of a seemingly airtight case, which hinges on the testimony of Morton's butler, who did not see or hear Chet leave the house, but claims he can pin down the time Chet left by an empty glass, which he insists smelled of Chet's cheap liquor. During a courtroom wine-tasting, to test the butler's sense of smell, Tony pours three liquids into separate glasses, then tricks him into identifying a glass of brandy as water. After discrediting the witness, Tony calls Ship to the stand to testify about the argument he had with Morton on the night of the party, forcing Ship to admit that Morton had been mishandling his financial duties. Producing evidence that Morton knew he had a brain tumor, Tony suggests that Morton committed suicide. When the jury concurs, Chet is acquitted and taken under the wing of Mrs. Allen. Joan, now realizing that Tony will sacrifice his career for matters of principle, reconciles with him.
