In 1813, Daphne Bridgerton makes her debut into the London social season. Queen Charlotte gives her high praise over other debutantes, including the three Featherington sisters. A new scandal sheet written by the mysterious Lady Whistledown circulates London. Marina Thompson, Lord Featherington's distant cousin, comes to stay for the season under the supervision of Lady Featherington. Simon Basset, the Duke of Hastings, returns to London after the death of his father; Lady Danbury coaxes him into joining the season. Anthony drives away many potential suitors for Daphne, except the detestable Lord Berbrooke. Marina picks up the slack, ittiating the Queen and Lady Featherington. After breaking up with his mistress, Siena Rosso, Anthony promises Daphne to Berbrooke, dismaying her. Lady Featherington deduces that Marina is pregnant. After Berbrooke accosts Daphne, and she hits him to protect herself, Simon arrives, and suggests they pretend to court in a mutually beneficial arrangement; Daphne agrees, attracting the attention of the ton.

Flashbacks reveal Simon's tragic childhood. After his mother died in childbirth, Simon was left under the control of his cruel father, who refused to accept that his only son was less than perfect. Lady Danbury came to his aid, assisting him in managing his stammer and supervising his education. On his father's deathbed, Simon vows he will never sire an heir in order to spite his father. In the present, the Queen grows more frustrated with Lady Whistledown's writings. Eloise Bridgerton and Penelope Featherington are confused as to how one becomes with child. Marina remains confined to her room, but shares with Penelope that her child was conceived in love with a man named Sir George Crane, who is fighting in Spain. Simon and Daphne's ruse works perfectly, but Anthony is upset. When Simon tells Anthony what Lord Berbrooke tried to do to Daphne, Anthony cancels his offer with Lord Berbrooke. Simon and Lord Berbrooke fight over Daphne's honor. Lord Berbrooke acquires a special license for his marriage to Daphne and threatens to ruin her name, but Lady Bridgerton intervenes and is able to get Lady Whistledown to reveal a scandal that forces Berbrooke to withdraw from London.

Simon and Daphne become closer, leading to Daphne turning down multiple proposals. Simon meets Siena, who invites him to see her after her next performance. Lady Featherington tries to match Marina again, but she waits for George to write back. Determined to prove that she is still the true ruler of London society, the Queen schemes to match Daphne with her nephew, the handsome and kind Prince Friedrich of Prussia. Lady Danbury tells Simon that he needs to propose to Daphne or step aside to make way for the superior match. Simon reluctantly calls off the ruse with Daphne. Viscount Benedict Bridgerton suspects Eloise of being Lady Whistledown. Anthony tries to take up with Siena again but she turns him down. George writes to Marina claiming that there was nothing between them, but unbeknownst to Marina, the letter was faked by Lady Featherington. Lady Bridgerton pushes Anthony to think about a match for himself. Simon decides to leave London ahead of schedule as a heartbroken Daphne embraces Prince Friedrich's attentions.

Prince Friedrich invites Daphne to the palace and gifts her a beautiful necklace. Marina is presented to older suitors in want of heirs in an effort to marry her quickly. Eloise decides she will find out Lady Whistledown's identity. Daphne attends a boxing match with Prince Friedrich. Marina is set up with an older suitor and is saved by Colin. At a sumptuous fete, Prince Friedrich prepares to propose but an undecided Daphne flees to the garden. Simon approaches her to say goodbye and apologize. Daphne, upset, runs into a hedge maze, followed shortly by Simon, and the two kiss passionately. Anthony interrupts and demands that Simon marry Daphne. Simon refuses and Anthony challenges him to a duel at dawn. Penelope is crushed by Colin's attention to Marina which causes a fight with Eloise. Anthony plans to use the duel to free himself from society and be with Siena. Lady Featherington discovers the extent of her husband's gambling debts. Daphne realizes that Cressida Cowper, her rival for Prince Friedrich's affections, witnessed what happened in the garden and races to stop the duel. Simon tells her that the reason he cannot marry her is because he cannot provide her with children. Weighing her options, Daphne firmly declares they will marry anyway.

Daphne and Simon petition the Archbishop of Canterbury for an expedited marriage license, but he refuses at the behest of the Queen. Prince Friedrich visits Daphne for closure. Anthony promises to take care of Siena even if they cannot be together, but local dressmaker Genevieve Delacroix claims she has left town. Money issues boil up at the Featherington home. Penelope becomes ever more jealous of Colin's attention to Marina. Cressida and Daphne confront each other. Benedict attends a party at the invitation of Sir Henry Granville. Lady Featherington intends for Marina to marry Lord Rutledge and orders her to cut out Colin. Simon and Daphne appeal to the Queen to allow for an early wedding; faced with losing her beloved King George III to his increasing dementia, the Queen is moved by Simon's impassioned plea. Simon and Daphne are married in a simple church ceremony. At the wedding reception, Marina gets a proposal from Colin, but with the request of a long engagement. The Queen takes interest in Eloise's investigation into the identity of Lady Whistledown. Lady Bridgerton and Daphne have a brief conversation about sex which leaves her with more questions than answers. Simon and Daphne leave for Clyvedon, but stay at an inn to avoid the journey after dusk. At the inn, Daphne finally confronts Simon over his avoidance of her, and the pair realize that they are in fact madly in love and consummate their marriage.

Simon and Daphne as the Duke and the new Duchess arrive at Clyvedon for their honeymoon and spend much time together, romantically and sexually. Daphne has difficulty building a relationship with the housekeeper Mrs. Colson. Colin announces his engagement to Marina, to his family's dismay. Daphne and Simon mingle with the villagers. Penelope tries to ruin the engagement by confiding in Colin that Marina is in love with another man. Colin suggests he and Marina marry sooner than their families desire by traveling to Scotland. Simon turns his attention to the books after hearing that his tenants' rent has increased. Daphne is told that she offended the village by not being able to pick a winning pig at the fair. Mrs. Colson reveals more about Simon's upbringing to Daphne. Penelope discovers that George's letter was faked, but Marina chooses to marry Colin anyway, intending to move on from George. Daphne, with the help of her lady's maid, realizes that Simon can have children, but does not want to. She assaults him in order to get pregnant, and confronts him afterwards, blaming him for being ambiguous about his inability. Lady Whistledown publishes Marina's secret, shocking Colin.

Simon and Daphne's dispute continues and Daphne decides to return to London after Lady Whistledown’s latest publication surfaces. Eloise prepares for her debut and continues to try to uncover Lady Whistledown in order to convince her to restore the Featherington name. Daphne arranges a chaperoned meeting for Colin and Marina. Simon decides to live separate lives if Daphne is not with child. The Queen is impatient with Eloise's progress in uncovering Lady Whistledown. The Queen throws the Featheringtons out of her luncheon because of Marina's scandal. Lady Danbury invites Daphne to a lively party with the married women of the ton, where Daphne, deciding to help Marina, tries to locate Sir George. To settle his debts, Lord Featherington approaches Will to convince him to throw his next fight; Will considers it. Anthony and Simon come to blows. Daphne discovers why Simon does not want to have children. Eloise realizes that Genevieve is the most likely person to be Lady Whistledown. Marina attempts to end her pregnancy and faints. At the opera Daphne begins menstruating, is therefore not pregnant, and cries in her mother's arms with Simon overhearing.

George's brother, Sir Phillip Crane, arrives with news that George died in battle. An unfinished letter from George reveals that he did love Marina and intended to return for her and their child. Phillip offers to marry Marina himself, but she turns him down. Eloise confronts Genevieve and, believing her to be Lady Whistledown, tries to convince her to write in the Featheringtons' favor. Daphne finds the letters Simon wrote to his father as a child and Lady Danbury fills in the blanks about Simon's childhood. Daphne begins to make amends with Simon, who is reconsidering what he wants after spending time with Daphne's younger siblings. Anthony reunites with Siena and invites her to Daphne and Simon's ball, but Siena tells Anthony to move on. Will throws the fight and receives his winnings from Archibald, who is murdered by his "associates". Marina realizes that she is still pregnant and after receiving insight from Lady Featherington, departs London to marry Phillip. Before Penelope can profess her love for him, Colin announces he is leaving for his tour of the world. The Queen sends her agents to capture Lady Whistledown, but Eloise is able to tip her off. A downpour interrupts Simon and Daphne's ball, but the couple reconcile, leading Lady Whistledown to declare it the best ball of the season. Anthony announces that he will find a wife without love. Eloise realizes that Genevieve is not Lady Whistledown, who is revealed only to the audience to be Penelope. Later, Daphne and Simon have their first child, a son.

Anthony starts seeking a wife, and immediately becomes one of the season's most eligible bachelors. He meets with several eligible ladies but no prospects intrigue him. Eloise is set to make her debut in society, but her presentation to the queen is interrupted by the return of Lady Whistledown's scandal sheets. On a morning ride, Anthony meets a young woman he later learns is Miss Kate Sharma. Lady Danbury has sponsored the Sharma family for the season, and Kate and her stepmother, Lady Mary, aim to find Mary's accomplished daughter Edwina a husband. Edwina wants a love match but is unaware, unlike Kate, that Mary's noble parents have offered access to the family fortune on the condition that she marry a peer. Kate overhears Anthony proclaiming to a group of other gentlemen that he does not care if he loves his wife so long as she is agreeable. The queen names Edwina the season's diamond, and Anthony resolves to make her his wife. Meanwhile, Portia struggles with her family's finances before the new Featherington heir, Jack, arrives in London.

Edwina has drawn the eye of several suitors, and Kate has taken charge of deciding which ones Edwina will meet. To Anthony's dismay, she is staunchly against Anthony courting her. Colin returns from his travels, while Eloise becomes intrigued with finding out Lady Whistledown's identity once again. After learning that Edwina will be at the horse races accompanied by another lord, Anthony takes his family and manages to ingratiate himself with Edwina. Queen Charlotte plans to use Edwina to unmask Lady Whistledown and invites the Sharmas to the palace. Benedict entertains the prospect of studying art. Anthony impresses Edwina with a speech at a soiree hosted by Lady Danbury much to Kate's dismay. Mme. Delacroix catches Penelope at the market.

In a flashback to ten years prior, the late viscount Edmund Bridgerton goes hunting with Anthony. When they arrive back at the house, Edmund is stung by a bee and dies. Subsequent flashbacks portray Violet's grief in the aftermath of Edmund's death and the pressure Anthony faced in becoming the new viscount. In the present day, the Bridgertons are at their country estate preparing for their prestigious annual ball, and Anthony has invited the Sharmas to stay for a few days ahead of the party. Along with Kate and Edwina, the siblings play a spirited game of pall-mall that results in Anthony and Kate muddying up their clothing while retrieving balls in the woods. To Kate's dismay, Anthony charms Edwina and tries to propose at dinner but backs out at the last moment. Benedict is accepted at the Royal Academy Schools while Eloise becomes interested in women's rights. Fearing that Jack will marry Cressida Cowper and oust the Featherington women from their home, Portia plots to have Prudence marry him. Penelope recruits Mme. Delacroix to be part of the Lady Whistledown scheme. In the gardens of Aubrey Hall, Kate is stung by a bee, causing Anthony to panic; the two almost kiss.

Guests begin arriving at Aubrey Hall for the Bridgerton ball. Unaware of their mutual attraction, Edwina encourages Kate to spend time with Anthony, thinking Kate's disapproval keeps him from proposing. Kate goes on a hunt with the men, where she and Anthony share another physical moment. Colin visits Marina, now Lady Crane, and meets her new husband. Marina's marriage is not happy, but she tells him to move on and that there are others that deserve his attention. Daphne tries to get to know Edwina but is unconvinced that she is a good match for Anthony. Portia arranges for Jack and Prudence to be caught alone to force them into marriage, but Jack reveals that he is secretly penniless and had been planning to marry Cressida for her fortune. Daphne catches Anthony and Kate in a compromising position in the library and urges Anthony to be honest with his feelings. As the Sharmas prepare to depart for London, Anthony proposes to Edwina, and she says yes.

Queen Charlotte heartily approves of Anthony and Edwina's engagement and even offers to sponsor the wedding. Both families go to promenade; Anthony becomes jealous when Kate goes on a boat ride with another man. Eloise sneaks out to Bloomsbury to attend a meeting about equal rights and meets Theo Sharpe, an assistant at Lady Whistledown's printer. Mary's parents, the Sheffields, visit London to meet Edwina, but at dinner, they display contempt for Mary and Kate, and their arrangement that Edwina should marry a nobleman comes to light. Defending all three of the Sharma women, Anthony orders the Sheffields to leave but is hesitant to continue the marriage; Kate convinces him to do so even as they admit to their feelings. Upon learning that several gentlemen are interested in investing in Jack's mines, Portia convinces him to take their money.

Preparations are underway for Anthony and Edwina's wedding. Edwina feels that Anthony does not love her; Daphne tries to steer Anthony into calling it off to no avail. Kate offers her mother's bracelets for Edwina to wear, but her sister tells her to wear them instead. At the wedding, Kate and Anthony cannot help but stare at each other; when Kate drops her bracelet at the altar, Anthony rushes to help her. Edwina realizes there is more to their relationship and runs away from the altar. A furious Queen Charlotte has the guests stay in the garden as Edwina composes herself. Kate tries to explain herself to Edwina, and Anthony confirms he is intent on the marriage; Edwina eventually decides that she cannot marry him. Kate and Anthony are left alone in the church and kiss. In the chaos, Lady Danbury and Violet reconcile, Jack makes potential business connections, and Eloise takes the opportunity to visit Theo once again.

Following the failed wedding, the Bridgertons and Sharmas, along with Lady Danbury, are shunned by the ton despite their best efforts. Queen Charlotte accuses Eloise of being Lady Whistledown and gives her three days to come clean, or risk punishment for her family. Eloise confides this in Penelope; in an attempt to protect her, Penelope writes that Eloise has been seen fraternizing unchaperoned with political radicals. The news embroils the Bridgertons in further scandal and nobody arrives at the ball they are hosting. Colin considers investing with Jack. Kate and Anthony sleep together in a gazebo on the grounds; the next day, Anthony attempts to visit Kate but is told that she has departed on a horse. Anthony follows Kate into a rainstorm on horseback, but she is thrown from her horse and knocked unconscious. Anthony calls to her and rides to her. The last shot shows her lying on the wet ground with her head next to a rock.

Kate is still unconscious, and Lady Whistledown has been suspiciously quiet. Portia convinces Jack to host a ball to celebrate the family's recent successes and invites the Bridgertons and Sharmas; Jack considers moving to America to start over before their fraud is discovered. Eloise ends her friendship with Theo after Penelope falsely tells her that servants have been gossiping about them. Benedict learns that he was likely accepted to the Academy due to a donation from Anthony. Kate awakens from her coma, and Anthony proposes to her, but she declines, citing her desire to return to India. Edwina reconciles with Kate and convinces her to attend the ball. After Penelope points out a piece of gossip about two guests, Eloise realizes she is Lady Whistledown and the two argue, causing Eloise to cut all ties with Penelope. Portia turns on Jack and sends him back to America while keeping most of the funds he had gathered for herself. Penelope overhears Colin telling other gentlemen that he would never court her and cries about her long time crush rejecting her and the end of her friendship with Eloise. Kate and Anthony dance at the ball, but the Queen neatly saves their reputations by claiming that canceling the wedding was her idea. Anthony and Kate declare their love for one another. Penelope decides to continue on as Lady Whistledown. After traveling for six months, Kate and Anthony, now married, join the rest of the Bridgertons for another game of pall-mall at Aubrey Hall.