The Couple at No. 9

In April 2018, Saffron "Saffy" Cutler, a 24-year-old graphic designer who is 14 weeks pregnant, lives with her boyfriend, Tom Perkins, in a Cotswold cottage at 9 Skelton Place in Beggars Nook, Wiltshire. When builders digging for a kitchen extension unearth a human skeleton, Saffy calls the police. Days later, a detective reports that two bodies have been found, one male and one female, dead since sometime between 1970 and 1990. The female died of blunt trauma to the head. The police need to interview the cottage's former owner, Saffy's grandmother, Rose Grey, who bought the property in 1977 and now lives in a care home near Bristol with Alzheimer's disease.

The cottage had been a surprise: Gran disclosed its existence during a lucid moment and had transferred the deeds to Saffy's mother, Lorna Cutler, who lives in Spain and gifted the property to Saffy. When Saffy visits Gran at the care home, Gran grows agitated, asking, "Is it Sheila?", a name Saffy has never heard. Gran mutters about "a wicked little girl" and an unknown man named Victor who "wanted to hurt the baby."

In Yorkshire, Theo Carmichael, a chef in his early thirties, visits his elderly father, Dr. Victor Carmichael, a retired medical consultant. Theo has a strained relationship with his controlling father and still grieves his mother, Caroline Carmichael, who died 14 years earlier in a supposed fall down the stairs. On Victor's desk, Theo finds a clipping about the Skelton Place bodies with Saffy's and Gran's names underlined and "Find Her" scrawled beneath. Victor refuses to explain.

Lorna, a 40-year-old former teenage mother, flies to England. At the cottage, she experiences flashes of childhood memory: a bedroom she recognizes as hers, a garden tree whose purple petals she used to mash into pretend perfume. That night, she finds evidence someone has been watching the house from the woods. When police interview Gran, she mentions a lodger named Daphne Hartall who lived with her around 1980 and makes a cryptic accusation about an unidentified woman: "Jean hit her over the head and she didn't get back up again."

Searching Gran's belongings, Saffy and Lorna find love poems with a pressed rose, photographs of toddler Lorna with an unidentified woman at the cottage, and a 1977 newspaper clipping about a woman named Sheila Watts who apparently drowned in Broadstairs, Kent. The article quotes a neighbor named Alan Hartall. Lorna tracks him to Broadstairs, where he reveals his sister Daphne died of cancer in 1971. Lorna concludes that Sheila faked her drowning, stole the real Daphne's identity, and moved to Beggars Nook as Gran's lodger.

A man who has been lurking near the cottage identifies himself to Saffy as Davies, a private detective whose client wants Gran to hand over a file. That evening, the same man attacks Lorna on the dark lane, demanding she ask Rose where she "buried the evidence" and threatening to hurt Saffy.

Theo, pursuing his own investigation, learns from his father's former practice partner that a young woman accused Victor of inappropriate conduct during a medical examination. No charges were filed, but the woman later died by suicide. Theo begins to suspect his mother's death was no accident.

Interwoven with the investigation are chapters narrated by Rose, addressed to "Lolly," Lorna's childhood nickname. Rose describes meeting Daphne on Christmas Eve 1979, offering her a room, and falling in love. On Easter Sunday 1980, the women begin a romantic relationship. The next evening, a man arrives at the cottage calling Daphne "Jean" and threatening to expose her true identity. Rose, believing he is attacking Daphne, stabs him with a breadknife. As he dies, he gasps, "You're both murderers now. She's Jean Burdon." Daphne persuades Rose not to call the police, and they bury him in the garden.

In the present, the male body is identified as Neil Lewisham, an investigative journalist who went missing in April 1980. Gran confirms Neil discovered Daphne was really Jean Burdon, a convicted child killer. In 1951, an 11-year-old named Jean Burdon was convicted of murdering a 10-year-old girl in east London. Saffy's father, Euan Cutler, a reporter at a national tabloid, locates archive files confirming Neil had been tracking Jean Burdon's new identity when he found her in Beggars Nook.

Theo and his wife, Jen, travel to the cottage. When Lorna describes her attacker, Theo goes pale: Davies works for his father as a security operative. Noting Lorna's striking resemblance to Victor, Lorna voices what they are all thinking: Victor may be her biological father, making Theo her half-brother.

Rose's narrative reveals why Victor is searching for Gran. He was never Rose's romantic partner but her fertility doctor. Rose and her then-partner, a woman named Audrey, had sought artificial insemination at his Harrogate clinic. After Audrey left during the pregnancy, Victor befriended the vulnerable Rose, then turned controlling and possessive, eventually revealing he had used his own sperm without her consent. Rose escaped, taking a folder from his study containing photographs of sedated female patients in compromising positions, her insurance against him.

Dental records confirm the female victim is not Jean Burdon. Melissa Brown, an elderly villager who knew Rose in the 1970s, visits the cottage with old photographs. She points out "Rose" in the images, and Saffy and Lorna are stunned: The woman Melissa identifies as Rose is the person they have always known as Daphne. The woman in the care home, whom they call Gran, is really Daphne. The identities were switched. DNA testing confirms the second body is the real Rose Grey, Lorna's biological mother.

In the small back bedroom, Saffy dislodges a mantelpiece to reveal a hidden cavity containing Victor's folder and a sealed letter from Rose to Lolly. After Saffy turns the folder over to police, Davies is arrested, and his testimony implicates Victor. Victor is charged with the murder of his wife, Caroline, admitting he pushed her during an argument; she fell down the stairs. He is also charged with sexual offenses and fertility fraud for inseminating patients with his own sperm without consent over many years. He is found guilty at trial.

In a final visit to the care home, Daphne, in a moment of painful lucidity, confesses. After Bonfire Night in November 1980, Rose confronted Daphne about her lies, ended the relationship, and told her to leave. When Rose turned away, Daphne grabbed a cast-iron kettle from the stove and struck her on the back of the head. Rose collapsed and died. Daphne assumed Rose's identity permanently, raised Lorna as her own, and buried Rose beside Neil. She moved to Bristol, renting out the cottage but never selling it lest anyone discover the graves. Neither Saffy nor Lorna reports the confession. Daphne dies days later.

One year on, the family gathers at the cottage. Saffy and Tom are raising their daughter, Freya. Lorna has returned to England and reconnected romantically with Euan. Theo and a pregnant Jen visit, now embraced as family, DNA having confirmed they are half-siblings. That evening, Lorna reads Rose's letter. The final page, which Saffy withheld from police to protect Gran, contains Rose's confession to killing Neil, her account of Victor's fraud, and her realization that Daphne had been manipulating her, including sending a farmhand to impersonate Victor and frighten Rose into fleeing. The letter ends with Rose's declaration of love for Lolly. Lorna clutches it to her chest, feeling she understands everything at last.