Annie Adams, who inherited the Gravesdown estate from her great-aunt Frances in the previous novel, sets out for an early morning walk on a misty November day, hoping to spark ideas for her writing. She is restless and lonely; Gravesdown Hall feels cold and empty without former gardener Archie Foyle and his granddaughter, Beth, who live nearby at Foyle Farm and formerly took care of the house. Annie suspects that the villagers of Castle Knoll are deliberately avoiding her, fearing she has been reading Frances’s infamous secret files on local residents.

At the edge of the estate grounds, Annie encounters an elderly woman with white hair and unusual green eyes. She realizes that this must be Peony Lane, the fortune-teller whose prediction of Frances’s murder set off the chain of events that made Annie the estate’s heir. Peony tells Annie that she has a fortune to deliver. Annie declines, but Peony warns her that she will eventually seek it out herself and hopes it will not be too late.

Peony instructs Annie to investigate the life and death of Olivia Gravesdown, who died alongside her husband Edmund and father-in-law Lord Harry in a car crash 60 years ago. Peony suspects that Olivia was murdered and believes Frances kept a file on her that might reveal information about the killer. She also tells Annie to find Frances’s file on Peony herself and to visit Archie Foyle, who has something Annie will need. Departing cryptically, Peony urges Annie to search Frances’s files for hidden murderers before vanishing into the mist.

In a diary entry, 18-year-old Frances Adams writes about her fixation on the fortune she received from Peony Lane that predicted her own murder. The previous summer shattered her: Her best friend, Emily Sparrow, disappeared, and she felt deeply betrayed. To fight what she believes is her fate rather than merely dread it, Frances has been studying mythology, astrology, and divination, hoping to outsmart the outcome. She identifies two adversaries—her future murderer and fate itself, which she believes Peony Lane represents—and resolves to track Peony down.

In the present timeline, walking to Foyle Farms, Annie reflects on large gaps in Frances’s diaries—several volumes are missing from the late 1960s. She consults Frances’s 1965 diary—which she acquired in the previous novel and now carries as a good-luck charm—and finds a brief reference to the Gravesdown car crash: Edmund was driving his father Harry and wife Olivia when he took a hairpin curve too fast, killing all three. Annie has never heard any local rumor suggesting foul play, but she decides to request the official accident report from Detective Rowan Crane, the local police detective who was an ally in her investigation in the previous novel. On her way to Archie’s, she stops to write in her own journal for about an hour, inspired by Peony’s appearance.

At Archie’s stone farmhouse on the River Dimber, Annie finds that Archie has anticipated her visit; two teacups are already set out, and the kettle is on. After they talk for a bit, Annie steps outside to take a rare call from her mother, who mentions a new romantic interest and cautions Annie about a “good behavior” clause in Frances’s will. Her mother also asks her to find and send Frances’s file on Peony Lane, which is odd, as her mother is in London and hasn’t had anything to do with Annie’s investigations in Castle Knoll.

Annie ends the call and hears a strange noise coming from the farmhouse’s waterwheel. It jams, and she calls Archie outside. Archie retrieves the obstruction—an ornate antique dagger with a gold handle set with rubies. Archie recognizes it, and Annie immediately links it to a story in Frances’s diary about a ruby-handled knife; Emily’s sister Laura “Birdie” Sparrow had always claimed that she had seen someone stabbed with that knife near the farmhouse.

In a diary entry, Frances recounts how Archie Foyle drew her into being interested in Gravesdown secrets. She had been in the Castle Knoll library studying news clippings about Peony Lane—finding only mundane stories—when Archie startled her and revealed that Peony Lane is not the woman’s real name.

Archie offers Frances information in exchange for her help persuading Ford Gravesdown to return the Foyle farm to his family. After Harry, Edmund, and Olivia’s deaths, Ford was the sole heir of the estate and raised Olivia and Edmund’s son, Saxon. Frances had been dating Ford, and Archie thinks she will have influence over him. He is open about his motive: Ford evicted the Foyles after Archie’s father had an affair with Ford’s wife, and Archie and his brother Eric were punished for their father’s choices. Despite this, Archie insists that the Peony Lane investigation and the Gravesdown family are inseparable.

He tells Frances that in 1961, Peony was arrested for vandalizing Edmund Gravesdown’s Bentley. She secretly cut the car’s brake cable, although she meant to cut the fuel line. After the vandalism, the car was repaired, then driven by Edmund, who could not stop at a curve and killed himself, his wife Olivia, and his father. Archie believes Ford suppressed any investigation into the accident and warns Frances that people who learn too much about the Gravesdowns tend to disappear.

In the present, Annie and Archie examine the dagger at his kitchen table. Archie confirms that the old village story that Ford stabbed his first wife was inaccurate. The knife has a long, thin blade attached to a gold handle with small rubies and two larger empty gem settings; its pristine condition suggests someone polished and placed it in the waterwheel deliberately.

When Annie asks how the knife connects to Peony Lane, Archie deflects. He names Eric as the person to ask, noting that Eric worked for the Gravesdowns and—around the time of the crash—was involved with both Birdy Sparrow and Ellen Jones, now known as Peony Lane. Archie then grows evasive, claiming the whole matter is fuzzy old memory. Annie says she will take the knife to Detective Crane; Archie agrees with visible reluctance.

To restart the conversation, Annie notices a library book on Archie’s shelf, decades overdue. This prompts Archie to reveal he was briefly married to the Castle Knoll librarian, Lucy Stokes, while in love with someone else. Years later, when Lucy became terminally ill, she asked him to take in her young granddaughter, Beth.

Annie then spots six small leather-bound notebooks on a high shelf, identical in style to Frances’s diaries and matching exactly the six-year gap in Frances’s journals from 1967 to 1972. Archie insists that they are farm ledgers and refuses her access. He concedes only that he and Frances spent months tracking Peony down together, and the fortune that ultimately mattered most to Frances was not her own—it was his.

In her diary, Frances recounts that she and Archie continued piecing together information about the crash: On May 15, 1961, Edmund Gravesdown lost control of his Bentley on a curve, killing himself, his wife Olivia, and his father Lord Harry. Ford Gravesdown, 20 years old, inherited everything and became guardian of Edmund’s seven-year-old son, Saxon. The article mentions rumors of Olivia’s infidelity, a rough-cut ruby found at the crash site, and a follow-up piece suggesting that Olivia tried to exit the car while it was moving because her body was found on the road.

Archie explains that at the time, Ford moved quickly to shut down any inquiry. Frances tentatively attributes this to protecting Saxon, but Archie is more suspicious. On the question of why Eric helped vandalize the car, Archie says Eric never gave him a reason. Frances plans to research Peony’s prison record and asks Archie to track the fate of the wrecked Bentley. She privately hopes the disappearance of her best friend, Emily, is connected to Emily’s search for her sister Birdy, who ran away several years ago. When Frances asks Archie about talking to Eric, Archie points him out working behind the bar of the Dead Witch, the town’s local pub. Eric catches Frances’s eye and smiles.

While Annie and Archie are talking, Archie’s granddaughter Beth arrives home—she and her wife Miyuki live at the farm with Archie. Seeing the knife on the table, she asks if she is interrupting. Annie says Archie was about to share the fortune he got from Peony Lane all those years ago.

With Beth settled in, Archie states the core of Peony Lane’s prediction: He will cause Peony’s death. He clarifies that causing someone’s death is not the same as murder. He then recites the full fortune:

The bird returns, but it’s you who are the bringer of death. You cannot cast the shadow of a shape that’s not your own. One death with three to blame, or three deaths with one to blame—the circle must complete. The list you seek is the right one—the foil, the arrow, the rat, the sparrow. It begins with a secret revealed, and ends with the secret destroyed (50).

Beth shares what Frances told her over the years: It took months to locate Peony, and by the time they did, Frances and Archie had been through considerable difficulty together. When they finally found her, Frances became furious—believing Peony was threatening Archie—and said things she could never take back. Annie asks Archie if this matches his account. He pauses, his eyes briefly moving to the knife, then confirms that it does.

Annie decides to bring the dagger to Detective Crane. Archie wraps it and lends her a vintage BMW from his new car restoration business, which she has invested in. He insists she keep the car. Driving toward the village, Annie passes the collapsed pub, now cordoned off by a cleanup crew.

At the police station, Crane encounters Annie in the car park; they share a relaxed exchange. Inside, the receptionist, Samantha, is curt with Annie, which is typical. Annie notices an elderly man in mechanic’s coveralls near Samantha’s desk. Samantha calls him Eric, and Annie suspects he is Archie’s brother.

Annie asks Crane for the accident report for the Gravesdown crash. Crane finds that the file has not been digitized and tells her to submit a request form. Annie mentions the rumored severed brake cable. Crane confirms that Peony Lane’s real name is Ellen Jones, and she was arrested in 1961 for vandalizing Edmund’s car. The record states that all damage was repaired before the crash, and she was never held responsible. Their conversation is cut short when Chief Inspector Toby Marks, a new senior officer, introduces himself. He dismisses the knife as irrelevant, refuses to authorize forensic examination, and tells Annie to take it home.