The Wrong Sister

The novel opens with an anonymous speaker watching an unnamed woman from her house, vowing to take everything from her.

Tasha Pritchard, a dental receptionist in the small English village of Chew Norton near Bristol, nervously prepares for a visit from her older sister Alice, a biochemist, and Alice's wealthy husband Kyle Campbell, a tech entrepreneur. The sisters have arranged a "life swap": Alice and Kyle will look after Tasha's nearly three-year-old twin daughters, Elsie and Flossie, while Tasha and her husband Aaron, a mechanic, spend a week in Alice and Kyle's holiday apartment in Venice. Tasha carries the lasting trauma of a family tragedy: Thirty years earlier, in October 1989, her baby sister Holly was abducted from her pram outside a village shop and never found.

As they leave for Venice, Tasha notices an asterisk drawn in blue chalk on the pavement outside her front gate but dismisses it. In Venice, the couple reconnects romantically. Tasha begins wearing Alice's designer clothes, feeling transformed. On their anniversary night, they are pursued through dark backstreets by a man with a knife who mutters something Aaron later translates as "You owe me." They escape, badly shaken, and Aaron suggests they were targeted because Tasha looked wealthy in Alice's clothes.

Hours later, a phone call from Aaron's mother Viv shatters everything: There has been a break-in at their house. The twins are safe with Viv, but Alice is in the hospital with a head injury, and Kyle is dead.

Tasha and Aaron rush home. At the hospital, Alice says Kyle went downstairs to investigate a noise and never returned. When Alice followed, she found him on the floor, was struck from behind, pushed hard, and blacked out. The police reveal that the patio doors were unlocked, with no signs of forced entry. When Tasha returns to the house, she finds a note on the doormat reading: "IT WAS SUPPOSED TO BE YOU" (93).

A second anonymous interlude reveals the stalker's perspective: The watcher had been following Tasha all summer but arrived too late to see the sisters switch places. The attack hit the wrong sister.

The investigation intensifies. Chloë Jones, a police family liaison officer, and her colleague interview the family. Tasha's neighbor Arthur describes seeing a tall blonde woman with a septum nose piercing near the front door on the morning the note appeared, a description matching Zoë Gleeson, a receptionist at Aaron's garage with whom Aaron has exchanged flirtatious texts. Aaron insists Zoë is just a friend. Meanwhile, Eve Milligan, Kyle's ex-girlfriend, tells Tasha that Kyle secretly met her on the day he died, saying he was scared and had gotten involved with corrupt investors. Eve adds that Kyle mentioned Alice was dealing with something related to her missing sister, implying Alice was actively looking for Holly. Alice furiously dismisses Eve as a liar and whispers that she has something important to tell Tasha but cannot say it in front of their mother.

Their mother, Jeanette, has flown from her home in France to be with the family, and senior detective Philip Thorne and Jones soon deliver a bombshell: Blood found on the living-room rug does not match any family member but shows enough genetic similarity to indicate it belongs to a close relative of Jeanette's. Alice reveals that months earlier she met a woman at a conference who subsequently sent typed letters signed "Holly," claiming to be their abducted sister and saying she was watching the family from the shadows. The evidence suggests Holly may have been present when Kyle was killed.

Interspersed chapters reveal the backstory of Bonnie Fairborn, a young woman who comes to suspect she may be the Harpers' long-lost sister Holly. After Bonnie's reclusive mother Clarissa dies, leaving a note reading "I love you, Bonnie. I always have. I'm sorry" (191), Bonnie's father Jack reveals she was adopted. In the attic, Bonnie finds newspaper articles about Holly Harper's 1989 abduction, baby clothes, and a photograph showing the bottom of their garden. Jack suspects the baby they legitimately adopted died while he was away working on oil rigs, and that Clarissa, overcome by grief, stole Holly to replace the dead child. The photograph marks where the original baby is buried. Jack gives Bonnie the name of Clarissa's estranged sister: Vivian Pritchard, Aaron's mother.

Back in the present, Zoë is found dead in the pond behind Tasha's house with a wound on her head. Aaron admits to Tasha that Zoë tried to kiss him and he rejected her. Tasha lies to the police to provide him an alibi.

Tasha travels to London for Kyle's funeral and discovers on Alice's laptop that Kyle has a brother, Connor Campbell, who is recovering from a heroin addiction and staying in a rehab facility, despite Alice's earlier denials that Kyle had any siblings. She also notices Alice's search history includes terms about chimerism, a rare condition in which one person carries two distinct sets of DNA. Alice eventually admits she lied about Connor to protect Kyle's reputation. The police inform Tasha that the Knight brothers, local petty criminals, admitted the blue asterisk was their mark for a planned burglary but deny killing Kyle. A tyre wrench with Kyle's blood is found in Zoë's garage, along with notes expressing obsessive hatred of Tasha, but neither Zoë's fingerprints nor her DNA are on the wrench.

Viv then arrives at Tasha's door with Bonnie, who has been working at Tasha's dental practice under the name Lola for two months. Jeanette recognizes her instantly. Viv explains that Clarissa was her sister and that she had long suspected the truth but convinced herself otherwise. Aaron also confesses to Tasha that colleagues at his garage, including Zoë, were involved with the Knight brothers in forging car identification numbers, and that his secretive meetings with Zoë were about this criminal activity. DNA testing confirms Bonnie is Holly Harper, but her DNA does not match the blood on the rug. Neither does Zoë's. Viv also confesses that on the night Zoë died, she confronted Zoë and pushed her during an argument; Zoë hit her head on a metal ledge but walked away alive. Viv later receives a suspended sentence for unlawful act manslaughter.

Two months later, Tasha is still troubled by the unmatched DNA. She calls Alice's friend Ellen Bright, a geneticist, who explains that Alice is a chimera: a person with two sets of DNA resulting from absorbing a twin in utero. Ellen confirms Alice knows about this condition. Tasha realizes the blood on the rug was Alice's second set of DNA, and that Alice deliberately withheld this information to make the police believe someone else had been at the scene.

A chapter from Alice's perspective reveals the truth. On the night of the killing, Alice waited for Kyle to go downstairs, pulled on gloves, retrieved Aaron's tyre wrench from where she had staged it, and struck Kyle from behind. Her motive was protecting her career: The health app she and Kyle had been developing, an electronic toothbrush designed to detect diseases through saliva, was fatally flawed, and Kyle's dealings with corrupt investors threatened to expose everything. After hiding the wrench, Alice slammed her own head into the TV cabinet to simulate an attack.

In the final chapter, Tasha confronts Alice on Hampstead Heath. Alice offers evasive non-denials and replies, "You're right. I'll never admit it" (367). She asks Tasha to stay silent for the sake of their mother, who has just been reunited with Holly. Tasha takes her sister's hand. As they walk across the frozen Heath, Tasha tells herself she has no choice but to keep quiet, and that if she keeps telling herself that, maybe she will finally believe it.