The novel opens with a prologue in which Emmeline "Emmy" Jackson, a prominent Instagram parenting influencer, believes she may be dying. Memories flash through her mind: her childhood with best friend Polly, meeting her husband Dan, their wedding, the births of their children Coco and Bear. She senses something terrible is about to happen and suspects it is her fault. The narrative jumps back six weeks and unfolds through three alternating perspectives: Emmy's, Dan's, and that of an unnamed woman whose motives are gradually revealed.
Emmy, known online as Mamabare, has over a million Instagram followers. She presents herself as a relatable mother who stumbled into influencing by accident, but the reality is calculated. A former fashion editor, she planned her career with her agent, Irene, studying Instagram parenting cultures to calibrate a persona of photogenic imperfection. She untidies her house before photo shoots, fabricates sleep-deprivation anecdotes, and engineers product crises to secure brand deals. Dan, her husband, is a novelist whose only book came out eight years ago. He classifies Emmy's public performances as what philosopher Harry Frankfurt called "bullshit": speech indifferent to truth. His stalled career has left the family dependent on Mamabare's income.
A third narrator attends one of Emmy's events, tries to speak with her, and is ignored. Seeing Emmy happy triggers a deep rage, and this person resolves to hurt her. The narrator pieces together the family's home address from a
Sunday Times photograph, spotting partial pub letters reflected in a mirror. Using details Emmy has disclosed online, the narrator identifies the pub as the Lord Napier in east London, then uses property websites and Google Street View to virtually tour the house and trace Emmy's daily routes.
When Dan takes Coco shoe shopping at a nearby mall, the narrator follows. While Dan is paying, Coco vanishes. After eight terrifying minutes, he spots her standing next to an older woman. By the time he reaches Coco, the woman is gone, but Coco clutches a grimy stuffed toy she did not have before. The narrator later reveals this was a test run: She gave Coco a teddy belonging to her late daughter Grace, walked hand-in-hand with the child through the mall, and considered harming her but stopped because she has something worse planned.
Irene assigns Emmy a new assistant, Winter Edwards, a micro-influencer. Emmy and Irene plan Coco's fourth birthday as a lavish brand-sponsored event. Dan, frustrated at being excluded, organizes a modest party at the local pub that barely anyone attends; the narrator sits unnoticed in the corner. At the official party, Emmy's best friend Polly, a quiet English teacher, arrives but Emmy barely spends time with her. Polly leaves abruptly; Emmy suspects her mother Virginia may have upset Polly with an awkward comment about children, though the precise cause remains ambiguous.
The family returns to find their house burglarized, and someone soon posts Coco's nursery address on a gossip forum. Winter is left to babysit, and while distracted by her phone, fails to prevent Coco from falling off a swing and spraining her wrist. At the hospital, Emmy secretly photographs sleeping Coco as "insurance" for any future public-relations crisis. Dan has lunch with his editor, hoping for interest in his novel, but his editor only wants to know if Emmy might write a book.
The unnamed narrator's identity comes into focus. She is a retired intensive care nurse and the mother of Grace, who is now dead. During a difficult pregnancy, Grace spent months on bed rest and found comfort following Instamums, especially Mamabare. Using her hospital access, the narrator stockpiles sedatives and medical equipment.
In therapy, Emmy discloses having two abortions before Coco, both unknown to Dan. Polly sends Emmy a personal email revealing that she and her husband Ben have suffered three miscarriages; Polly notes she had hesitated to share, partly to spare Emmy guilt over the abortion. Emmy is moved but sets the email aside. Winter realizes the stolen laptop had all of Emmy's passwords on a Post-it note, giving the thief access to private photos and messages. When Irene tells Emmy she must submit a personal video for a BBC Three documentary about baby loss that afternoon, Emmy reads Polly's account nearly word-for-word as her own into the camera.
Dan discovers an Instagram role-play account, a type of account in which strangers repost stolen photos of children under fabricated identities, using images of Coco under the name "Rosie." The BBC shares Emmy's audition video with journalist Jess Watts, who shows it to Polly. Devastated, Polly tells Jess the truth. The
Mail on Sunday runs the story with the headline "THE INSTAMUM WHO STOLE MY DEAD BABIES." Irene devises an excuse and plans a digital detox retreat so Emmy can disappear until the scandal subsides.
The narrator's full motive is now revealed. She had bought Grace a ticket to a Mamabare event, where Grace asked Emmy about cosleeping, the practice of sharing a bed with an infant. Emmy said it was perfectly fine. Grace adopted the practice, and one night her long hair wrapped around baby Ailsa's neck as they slept, cutting off the infant's air supply. Grace's husband Jack found Ailsa dead the next morning. Months later, the narrator saw Emmy on television saying cosleeping was never something she had tried, directly contradicting her earlier advice. Grace, devastated by Ailsa's death and her marriage's collapse, eventually died by suicide. The narrator found her body.
The narrator intercepts Emmy's transport to the retreat by posing as her personal assistant and arranging a different cab. Emmy arrives at Grace's old home, where the narrator serves tea laced with propofol, a powerful sedative. Emmy loses consciousness. The narrator places Bear beside her on the bed and hooks Emmy to an intravenous drip of midazolam, another sedative, to keep her unconscious. Her plan is to let Bear die of dehydration while Emmy lies beside him, mirroring how Ailsa died next to sleeping Grace. The narrator also writes a detailed confession letter explaining her identity and motives, intending to leave it on the living room table for Emmy to find when she wakes.
Dan traces the role-play account to a teenager who bought the photos via PayPal. The PayPal account belongs to Winter, who staged the break-in and sold the photos to pay off debts. While Dan confronts the teenager, Irene calls: Emmy and Bear never arrived at the retreat and have been missing over 72 hours. Irene posts an appeal on Emmy's Instagram, and the online community analyzes Emmy's final Instastories, identifying landmarks to trace her route into the Surrey countryside. Dan and Irene follow the trail to a remote house, where they find Emmy drugged and barely alive. Bear lies next to her, gray and unmoving.
The epilogue jumps forward 18 months. Bear survived and is healthy. Emmy and Dan have written a bestselling memoir, and Emmy has a family talk show. Dan runs her Instagram with two million followers, and Emmy is pregnant with a third child. Irene pocketed the narrator's confession letter before police arrived, and the published memoir omits the true motives, portraying the narrator as a motiveless stalker. Only in the epilogue is the narrator named: Jill. Emmy knows the truth but suppresses it for the brand's sake.
In the final section, Jill narrates. She drove to a beach intending to drown herself but stopped, not from fear, but from fury that her plan made Emmy more famous than ever. She lives a cash-only existence, legally presumed dead. She is at the literary festival where Dan reads from their memoir, sitting in the fourth row, unrecognized. The novel ends with her promise that she is still watching, still waiting, and could be anywhere near the family at any time.