The episode unfurls in the picturesque Provençal countryside, where Marie (Vanessa Ifediora), shrouded in mystery, orders a coffee at a quaint café. Sandrine (Ludmilla Makowski) slides into a seat beside her, curiosity piqued, inquiring about Marie's identity. Marie, enigmatic as ever, hands over a folder, which Sandrine scrutinizes intently, demanding to know its origin. Marie, declining to reveal her name, hints that the circumstances should have been different yet underscores the urgency of Sandrine's awareness. Nearby, a father reprimands his daughter loudly in a booth. Seizing the folder, Sandrine makes a beeline for the exit but pauses, intercepting the girl’s plight with empathy. She reassures her, encouraging her not to repeat the mistake, and promptly dumps a coffee into the man’s lap, eliciting a mischievous grin from the girl.
Two months leap forward to the serene landscapes of the Cotswolds, England. Zoe Morville (Sally Bretton), on her way to her shop, warmly greets Mr. Evans. Stepping inside, she finds Susannah (Natalie Britton) attending to a dissatisfied client. Susannah inquiries about Zoe's progress in finding an au pair, to which Zoe laments her futile search, blaming it on Dr. Chris Morville’s (Kenny Doughty) suggestion. The client's wedding gown, still not to her liking, prompts Zoe to seize it and bolt out the door, offering a ride to Amber Morville (Margot Pue) and Raye (Ebimie Anthony), who politely decline. Pulling into her driveway, she's met by Noah Morville (Ripley Barden), pedaling his bike with vim. He suggests pizza for dinner, and though hesitant, Zoe agrees.
Indoors, Zoe ponders over a christening gown, her fingers dancing on a sewing machine as she adorns it with delicate butterflies. Later, she visits George (David Suchet) to administer his insulin, cherishing their moments together despite his concerns about her miscarriage. He praises her resilience. Upon exiting, Zoe notices an ajar storage gate, a hint of unease creeping in. As dusk descends, a shadowy figure seems to track her return home. Immersed in a bubble bath later, Chris joins her, inquiring about their children. Zoe confesses that three years on, she still feels like an imposter in Eva’s former role. Chris reassures her of the kids' affection, and they share a bath together.
Meanwhile, Amber turns down Zoe’s smoothie, prompting Chris to take a sip, only to find his shirt stained. Noah, seizing the moment, requests the shirt, and Zoe frantically scrubs at the stain, determined to keep him on her side. Chris emphasizes the need for an au pair, but Zoe hesitates, wary of bringing a stranger into their still-bonding family. After Chris kisses her goodbye, Zoe manages to slip the damp shirt over Noah’s head, who complains about its wetness. She reaches for the hairdryer, but Noah dashes off to school on his bike, only for the brakes to malfunction. Losing control, he narrowly avoids a collision and crashes into a rock, thrown from his bike.
Zoe apologizes to Sylvie (Jean Van Sinderern Law) for the unfinished gown, her baby cooing softly in its carrier. A phone call interrupts, alerting her to Noah’s accident. She rushes out, finding Noah seated beside Sandrine, who urges him to return to school, proudly displaying his battle scars. Smiling, Noah agrees, and Sandrine loads the bike into the trunk. Zoe receives an urgent call from Chris about George's emergency alarm. Grateful to Sandrine, she speeds off to find George unconscious on the floor. Zoe checks his blood glucose, finding it critically low. Chris administers insulin, questioning if she had given too much earlier. George awakens, scolding Chris for the double injection. Sylvie calls, informing Zoe of her arrival at the studio. Briefing George about Noah’s mishap, Zoe dashes out once more.
Flashbacks reveal Sandrine's sinister actions as she meddles with George's insulin and tampers with Noah's brakes. Her constant griping about the gown echoes through the narrative. Zoe informs Chris that she is open to the idea of hiring an au pair, and a young woman is en route for an interview. However, Sandrine, intercepting her, coldly informs her that the position has already been filled. Chris peruses through the resumes, unaware of the drama unfolding. Amber makes a cutting remark about Zoe feeling like an outsider in their home, to which Zoe responds with a forced laugh.
Sandrine arrives for what seems to be an interview, but Zoe recognizes her instantly and alerts Chris to the fact that he had once assisted Noah. Sandrine feigns expertise in managing her grandmother's diabetes, an ominous parallel to her earlier actions. Later, she incinerates files and photographs belonging to the Morville household and family, her true colors showing through.
In the studio, where Zoe is meticulously altering a dress for Sylvie, she entrusts Sandrine with checking on George during their upcoming camping trip. Sandrine, handling the cherished christening gown, expresses her admiration for it, unaware of its tragic history. Zoe reveals that the gown was intended for their lost baby, the result of a mid-term miscarriage. Sandrine, ever manipulative, encourages Zoe to complete it for their next child, disregarding Chris's reservations.
As Sandrine heads to George's room, she overheads Amber and Raye whispering about Raye's pregnancy. This piece of information seems to ignite something within her. Zoe later pressures Chris to consider another embryo transfer, but he stands firm in their earlier decision. Zoe argues that it was his decision alone, not hers, as she eavesdrops from the hallway. George warns Zoe of the risks associated with another pregnancy, hinting that Chris's fear stems from the potential loss of his wife once more. Zoe ponders how Chris would react if she conceived without his knowledge.
On the way to school, Noah confides in Sandrine about the tensions between Zoe and Amber, specifically over a torn dress. Tyler teases Noah about needing a babysitter, unaware of the hidden dangers lurking in their midst. At the hospital, Dr. Vaughn requests an updated consent form, and Zoe promises to bring it on her next visit. Vaughn prescribes pre-transfer medications, setting the stage for potential conflict.
Sandrine, lurking in the shadows, slices Sylvie's dress with a knife and hides just before Zoe enters. She watches Zoe swallow her medication and pick up the christening gown, her plan beginning to take shape. Sandrine seizes the moment, opening the door and offering Zoe lunch, her intentions far from innocent.
Later, Chris gripes about taking medication, but Zoe insists he needs the rest, reminding him of their impending camping trip. She broaches the topic of having another child, but Chris brushes her off and retreats to bed. The next morning, Sylvie arrives to collect her dress, only to find it ruined. Zoe storms into the house, accusing Amber of destroying her dress, while Sandrine watches with a sinister smile. Chris steps in to mediate, but Sandrine catches up with him, feigning concern for Zoe's well-being. He attributes her stress to overwork, unaware of the treachery brewing beneath the surface. Sandrine subtly suggests that Zoe should refrain from working on the christening gown, her true intentions hidden beneath a veneer of concern.
Sandrine issues a chilling ultimatum to Tyler: back off from Noah, or face the consequences. Amber and Raye, their ears catching a sudden scream, duck for cover behind a towering tree. In an instant, Sandrine forces Tyler to the ground with a rough shove before disappearing into the distance. Zoe.
Entering Zoe's studio stealthily, Sandrine pries open a drawer concealing Zoe's IVF medication. Moments later, Chris arrives, his attention drawn to a delicate christening gown. Zoe steps in, noticing the ajar drawer, while Sandrine eavesdrops from the doorstep. Chris extends an invitation for lunch, which Sandrine politely declines, citing pressing work commitments. She hastily slams the drawer shut as he exits.
Biting into an apple, Sandrine finds Noah at her side, relating Tyler's apology tinged with suspicion of foul play. Noah jokes about someone beating him up, prompting Amber to declare the perpetrator a psychopath preying on children. Noah inquisitively asks Sandrine if she's behind it, to which she responds by querying if he'd dare tell his parents. He shakes his head vigorously.
Later, Raye confides in Amber about her mother's ignorance regarding her pregnancy. Sandrine bursts in, her congratulations echoing through the room, vowing to keep Raye's secret. Meanwhile, Zoe is in the midst of packing when Sandrine arrives, Tasking her with assisting Noah while dashing off to a meeting.
Sandrine slips sleeping medication into George's soup, watching him cheer a cricket match obliviously. As the medication takes effect, George stumbles up the stairs only to collapse backward. Sandrine observes the scene unfolding through the window with a calculated gaze.
At the hospital, Zoe informs Vaughn of her plan to have Chris sign the consent form over the weekend. As Chris chats with a medical staff member, Sandrine calls, alerting him to George's condition. Shortly after, Chris searches frantically for George's insulin, only to find it missing. Sandrine hints at Zoe's stash in her studio, then slips the insulin from her pocket once Chris has left. Chris scours Zoe's studio drawers, stumbling upon her IVF medication. Sandrine reveals she has George's insulin, as EMTs whisk him away in an ambulance.
Chris confronts Zoe about the medications, with Zoe reminding him of her attempts at communication. He accuses her of going behind his back, to which she responds with her yearning to be a mother. He insists she already is one, but she counters that they aren't her biological children. Overhearing the heated exchange, Noah flees, prompting Chris to chase after him. Zoe notices Amber peering from an upstairs window, unaware of the unfolding drama.
Sandrine offers Chris food for their upcoming camping trip as Zoe pulls into the driveway. Amber expresses concern for Zoe's safety, to which Chris reassures her with Sandrine's presence. As Sandrine chops carrots, Zoe arrives, slipping something into her pocket. Zoe informs Sandrine that George is stable but needs monitoring. Sandrine, unseen, spikes Zoe's wine. Zoe takes her medication, wiping away steam from the mirror, only to be startled by Sandrine's sudden appearance. Sandrine serves the poisoned wine, turning up the music, and begins to dance. Sandrine herself drinks the spiked wine and feels sleepiness creeping in. She catches a glimpse of her scar in the mirror as Zoe drifts off in the bathtub. With a sinister whisper, Sandrine declares, "You have no idea how long I've waited for this moment," and forcefully pushes Zoe's head underwater. Zoe lies still, her breaths unnoticed, her life hanging by a thread.
