The narrative returns to two months earlier, at Clarke Manor, where Eleanor Clarke receives Lady Duxbury’s private invitation to the Secret Book Society. Eleanor hides it, recalling her first meeting with Lady Duxbury three years earlier at a charity event, where she had inadvertently revealed her love for Mansfield Park. Eleanor guesses this is the reason Lady Duxbury has invited her to her parlor.

At breakfast, Eleanor’s controlling husband, Cecil, opens her mail, including Lady Duxbury’s formal invitation to tea, sent as a cover for the book club meeting. Cecil allows Eleanor to attend but demands she wear diamonds to the event to show off his wealth. Eleanor cannot wait for June, when Cecil will travel to Peru, giving her respite from his bossiness.

American heiress Rose Wharton, another of Lady Duxbury’s invitees, arrives at Duxbury Place. She recalls lending Lady Duxbury A Masque of Poets at a ball, which began their acquaintance. Rose meets Eleanor, and her attempt at a jewelry joke falls flat, highlighting her awkwardness. Davies announces Lady Lavinia Cavendish, who is attending in her mother’s place. Lady Duxbury’s cat, Otis, curls up inside a glass vase.

Lady Duxbury outlines the society’s purpose as a private haven for women whose reading is restricted. She notes that many of her staff come from poverty and rough trades. Rose admits that she feels lonely in England. Eleanor and Lavinia affirm a desire for friendship, and the group welcomes Rose into their circle.

After tea, Lavinia borrows a copy of Jane Eyre from Lady Duxbury’s library. When Lavinia returns home, her father and brother Robert taunt her with gossip that Lady Duxbury murdered her three husbands. Lavinia defends Lady Duxbury. In her room, she examines the book’s scorched cover and recalls Robert throwing this same copy into a fire weeks ago, after which she punched him.

In response, Lavinia’s father removed her books to suppress her emotions and avoid any hint of mental illness associated with their family. Wearing a small belladonna embroidery as a private reminder to hold her tongue, Lavinia receives her mother, who recognizes the book as one her father sold. Her mother explains that Lady Duxbury likely bought the family’s library and quietly encourages Lavinia’s secret friendship.

The following evening, Eleanor hosts a ball. Cecil flaunts his wealth by using expensive electric lights instead of candlelight. Eleanor greets guests beside an already drunk Cecil. Eleanor finds Rose and Lavinia, and the three women talk easily. They note Lady Duxbury’s absence, and Rose shares that Duxbury’s staff includes former poorhouse workers and pugilists.

Across the room, Cecil lifts his hand in a silent summons. Eleanor excuses herself, protective of her new friends, and returns to his side.

Lavinia feels awkward at the ball when an earl orders her to smile. A young gentleman called William Wright intervenes, deflects the insult with wit, and leads Lavinia away, claiming a prior acquaintance with her to satisfy propriety. After William leaves, the crowd swells, and Lavinia, who has claustrophobia, begins to have a panic attack.

Eleanor notices and guides Lavinia to a quiet parlor that has a famous painting. The calm space allows Lavinia to relax, and she and Eleanor discuss the painting’s image of a storm-tossed world. The moment strengthens their bond.

Rose arrives late at Lady Duxbury’s for the next book society meeting. Duxbury admires Rose’s black boots, which have a secret pocket. Rose tells the women the boots are from America, moving to shut the drawing-room door for privacy. Duxbury reacts sharply, insisting it stay open; since she was physically confined in the past, open doors make her feel safe. The group discusses Sense and Sensibility, and Duxbury asks the women why their reading is restricted.

Rose explains that her husband, pressured by his brother, tries to curb her supposedly “loud” American ways, creating marital strain. Lavinia emphatically defends Rose’s open, honest demeanor. Buoyed by the women’s candor, Eleanor prepares to speak about her own domestic situation.

As Eleanor hesitates to speak, a bruise on her arm is visible. Lady Duxbury quietly leads the group to her library. In private, Lady Duxbury acknowledges the bruise and tells Eleanor that the violence is not her fault. She points to a loose knot in the bookcase woodwork. When Eleanor presses it, a secret panel opens.

Inside lies Lady Duxbury’s diary. Eleanor hides the diary inside a volume of Jane Eyre, then opens to the first page. The entry begins with a declaration that the writer has been a captive, signaling the gravity of the account.

In the diary, a young Clara (Lady Duxbury) describes fleeing her home disguised as a maid to avoid marrying Viscount Morset. At the train station, a couple offers her shelter but is attempting to lure her into a brothel. A bookseller named Elias intervenes, fights them off, and explains their scheme. Elias walks her home while she maintains her maid disguise. She and Elias begin to meet secretly at the bookshop and fall in love.

A few days later, Rose attends a luncheon at the home of Mrs. Baskin, a socialite. Rose senses the invite was a mere courtesy, since she is left to stand by herself until Eleanor approaches and introduces her to Mrs. Edwards, who leads a local charity. Mrs. Edwards recruits Rose to the Society for the Advancement of the Poor.

During the meal, Eleanor sits with Rose, and Rose realizes that Eleanor is using her own social standing to protect her. The other guests begin to accept her.

Eleanor arrives early, wearing a salmon velvet dress, to the next tea at Duxbury Place. A maid named Mary, who has visible scars, serves tea. Rose and Lavinia thank Eleanor for her support during the last few social events. Eleanor explains that her keen observation skills come from monitoring her husband’s moods. She admits that her husband is intolerably cruel.

The women offer solidarity and move to the library. Eleanor retrieves the diary and reads the next header, which states that its writer has been captive for 52 days.