Lilian reaches Swanage and walks to Rosemark House, an imposing Tudor manor. Two women both introduce themselves as Abel Bell. They reveal they are Deidre, seventy-four, who began writing under the pseudonym Abel Bell at 18, and her granddaughter Agnes, who now writes the books. Lilian recounts everything: the books, Devlin, her father’s death, the hidden pages, Isabel’s story. Without commenting on all she has revealed, Deidre and Agnes invite Lilian to sleep.

In the morning, Deidre and Agnes give Lilian the Bell book, When Love Lies Unsung. The pinprick code reveals it is the sixth in the set (now only the second remains to be found). They have already removed and read the hidden pages and hand them to her in an envelope, asking only that she return one day to share the rest of the story. Lilian asks them about the auction at which they purchased the book and they explain that they were there, although Grieves did the bidding on their behalf. The price was so high because someone else was also bidding desperately on the novel: a woman named Julia Chatton, daughter of Silas Chatton. Lilian realizes that Silas Chatton must be the uncle mentioned in Isabel’s papers and that Julia is therefore her cousin.

Lilian realizes Julia is most likely the one employing Devlin and wonders why she is so desperate to obtain the books. Deidre recounts events from the 1840s and 1850s, when she was living in London and beginning her career as a writer. Silas and Malcom Chatton were wealthy and powerful brothers; Malcom’s daughter, Isabel, was a mysterious figure who was rumored to be beautiful but reclusive. Around 1851, rumors flew about mysterious events connected to her but ended with an official story that she and her father had moved to America. Silas’s son, Julian, died and he eventually remarried and fathered Julia. These events align with what is described in the letters, and Lilian tells the two women about what she has learned about Isabel’s secret marriage and pregnancy. She sits down to read the new pages.

The pages continue Isabel’s narrative, resuming with her father berating her for falling pregnant. He locks her in her room for months. Beauchamp breaks the engagement, so Silas and Malcolm plot to marry Isabel to her cousin Julian after the birth, with the child to be sent to an orphanage. The engagement is announced in a newspaper article. Isabel continues to secretly correspond with William and sometimes sees him lurking outside her house.

Isabel gives birth to a son, Isaac William, on 15 May 1852. Isabel’s father orders Dr. Ashburn (the doctor who attended to Isabel’s pregnancy and delivered the baby) to kill the infant. Ashburn takes the baby, promising Isabel to keep him safe; the doctor later explains that the baby is being cared for by his wife. By then, Isabel has received word of the lodgings where William is staying and asks Ashburn to take the baby to him. She is also asks Ashburn to find a lawyer he trusts and bring him to house to witness her testimony. Isabel is preparing to stockpile the documents (marriage certificate, birth certificate, and notarized and witnessed testimony) to prove her son’s legitimacy.

Meanwhile, Isabel’s cousin Julian has been found shot dead. Silas is desperate for vengeance and Isabel overhears him theorizing that William must have killed Julian, since the murder happened shortly after Julian and Isabel’s engagement was publicly announced. When Malcolm makes callous comments about Julian’s death, the two brothers end up fighting and Silas beats Malcolm to death. The crime is quickly covered up but Isabel knows that she, William, and their son are all in serious danger. Isabel dictates the document before Ashburn and notary Harold Pierce, enclosing the marriage and birth certificates to prove Isaac’s inheritance. The pages Lilian has been reading are a legal testimony (this explains the initials on each page) and Isabel’s message to William. 

Isabel ends with hope that her infant son will be established as her father’s legal heir and the three of them will live safe and happy. She alludes to a puzzle that will tell him where to find her.

Lilian discusses the pages with Deidre and Agnes and decides to visit Dr. Ashburn in Bath, believing his late father attended Isabel. They give her the book and pages and ask her to return one day with the ending. At the station, Lilian spots Devlin on the platform but boards the train unseen. She travels to Dr. Ashburn’s home in Bath, where she explains that the burned book he gave her weeks ago contained documents written by Isabel Chatton. The doctor confirms that his father worked for the Chatton family up until the time of Malcolm Chatton’s death and confirms that it is father’s initials on the document. Then he tells her he knows the story of the missing child and the fate of William Heathfield.

Dr. Ashburn explains that his father kept detailed journals and that he has looked through them. He directs her to a journal from early 1852. Lilian reads about how Dr. Ashburn the elder took Isabel’s baby, Isaac, to his own wife. There is also a journal entry describing his plan to meet with William Heathfield after Isabel gave him William’s address. During their visit, Ashburn tells William about the birth of his son; the latter begged for help reuniting with Isabel and his son.

There is an entry from when Dr. Ashburn learns of Malcolm Chatton’s death: The death is described to him as injuries resulting from surprising intruders, but Isabel later tells Ashburn the truth—Silas killed Malcolm. Ashburn knows that Isabel is in danger and promises to help her. Unexpectedly, he is summoned to Silas’s home. Dr. Ashburn diagnoses Silas with second-stage syphilis and learns that Silas’s men were hunting William; he sends a note of warning to William’s lodgings. A few days later, fearful for William, Dr. Ashburn returns to the lodgings and finds William severely beaten and clutching a smoldering book pulled from the fire. Ashburn stays with William as he dies. Afterwards, he is more resolved than ever to keep Isabel and the baby safe.

Lilian rejoins Dr. Ashburn in the library. He explains his father told Isabel about William’s death and that it would be safest if he kept Isaac. Ashburn raised Isaac as a ward, claiming he was an orphaned distant relation. Isaac is now a doctor at a New York hospital. Ashburn also explains that when Isabel asked about her testimony or any books by Abel Bell, his father tried desperately to find these materials. Ashburn also doesn’t know what happened to Isabel; after 1852, she is not mentioned again in the journals.

Eventually, the elder Dr. Ashburn was able to track down one novel from the set, but he could not figure out what was special about it. Dr. Ashburn presents this book to Lilian: the novel is titled The Lyre’s Broken String and the pinprick code indicates it is the second book in the set. Lilian slits the endpaper and removes the final pages, along with Isaac’s birth certificate and Isabel’s marriage certificate. She reads the opening of Isabel’s witnessed testimony, confirming that Isaac is the legitimate Chatton heir.

Ashburn reveals that Julia Chatton, Silas’s daughter, previously came to him demanding his father’s journals and asking about Bell’s novels. He also states she married a bookbinder named Mohan Chand. Lilian realizes Mrs. Chand, the woman from the train, is Julia Chatton.

Lilian realizes that after she chatted with Julia/Mrs. Chand on the train, the latter knew her name and the name of her father’s business. The attack on her father was likely revenge for having stolen Orpheus in the Tower from the Chand shop. She writes a letter to Julia, challenging her to meet at Silas’s London home. Dr. Ashburn agrees to deliver the letter along with the copy of his Bell novel but warns her not to underestimate Julia. Lilian dines with Ashburn and his wife and stays the night, sleeping fitfully with nightmares of Julia and Devlin.

Lilian arrives at Silas Chatton’s empty London townhouse. Julia admits her and leads her to a small library. Lilian accuses Julia’s father of having murdered Malcolm and William but Julia counters that he did what was necessary to protect his family. Silas spent years looking for William and for the Bell books but could never find them. She reveals that Silas kept his own papers and while reading those, Julia learned about Isabel’s testimony. Julia also explains that she has a four-year-old son who has the strongest claim to the Chatton fortune, so long as the existence of Isabel’s son is never confirmed.

Lilian presents the pages of the testimony; Julia demands the certificates. Lilian lies that she has them in her bag and then threatens Julia with a knife, explaining that “I want the pages and I want you to leave me alone” (361). Julia throws the pages into the fire and strikes Lilian with a pistol. The two women struggle and Julia is knocked unconscious. In the struggle, fiery sparks have spread from the fireplace and a severe fight starts. Lilian tries to awaken Julia, who insists on continuing to fight. When Julia’s hair catches on fire, Lilian accepts that she cannot save her and flees from the library Lilian escapes through a back gate as the house burns, consuming Julia and the handwritten testimony.

Lilian travels back to Oxford and collapses at Harry’s door. She wakes in the hospital with burns and an injured hand. As she recovers, she reads a newspaper article about the fire and Julia Chatton’s death. Harry comforts her and explains that while Devlin tried to attack him, some of the other printers drove him off. Without Julia paying him, they surmise that Devlin won’t bother them any further. Lilian tells Harry everything, including her night with Charlie; Harry asks for time to think.

Lilian returns to the bookshop and finds a letter from the bank stating her father’s debt has been cleared by an anonymous payment. She visits Caxton at his home, where she meets his partner Robert and learns Caxton paid the debt as an investment, offering her a partnership in a combined bindery and bookshop. She accepts. That evening, examining the complete set of six books, Lilian solves a double acrostic composed from the first and last letters of the titles: ATHLOW GRANGE.

Lilian writes to Ambrose Fane, who quickly replies identifying Athlow Grange as an estate near Fairford in Gloucestershire. Dr. Ashburn sends the birth and marriage certificates to her and Lilian travels to Athlow Grange. The maid who answers is Daisy, Isabel’s lifelong companion. Inside, Lilian meets Isabel Chatton herself, now in her seventies. After sending the letter and testimony to William, Isabel fled to the remote manor house, hoping William would come to her. Lilian recounts everything she has discovered, returns the certificates, and tells Isabel that Isaac is a doctor in New York. Isabel agrees to write to him; she will let Isaac decide if he wants to contest the will for the Chatton fortune or let it pass to Julia’s young son.

Lilian asks about Julian’s death and Isabel explains that after learning of the engagement, William was enraged and challenged Julian to a duel. Isabel and Daisy snuck out to watch. After Julian was shot and fatally wounded, Isabel helped William to hide evidence of the duel. Isabel speaks of forgiving William’s mistakes. Lilian leaves resolved to see Harry, hoping he can forgive her.

Lilian reopens the bookshop and begins her partnership with Caxton. Outside the shop one evening, Harry waits for her. They reconcile, each apologizing for past wrongs. Lilian tells him about Isabel and that the mystery is finally over. Harry produces a silver-bound book he found beneath a floorboard at the press and asks her to examine it.