Zoe O'Connell, a 28-year-old single mother in London, is struggling to hold her life together. Her four-year-old son, Hari, has been diagnosed with selective mutism, a social anxiety disorder so severe that he does not speak even to her, communicating only through gestures and silent tears. A consultant speech therapist offers reward-based strategies but no quick fix. The same day, Zoe returns to their cramped bedsit in Wembley to find a rent increase she cannot possibly pay.
Hari's father, Jaz Mehta, is a charismatic but irresponsible aspiring DJ who has never properly lived with them. He has lost his job and cannot contribute. Jaz's older sister, Surinder Mehta, a Birmingham businesswoman, learns for the first time about her brother's secret child. She connects Zoe to her old flatmate Nina, who runs a mobile bookshop in the Scottish Highlands and needs maternity cover, and to Mrs. MacGlone, the housekeeper at The Beeches, a crumbling baronial estate on Loch Ness. The estate is owned by Ramsay Urquart, the reclusive laird, or landowner, whose wife vanished two years earlier. Surinder arranges a package: part-time work with the book van, a live-in au pair role, and a free nursery place for Hari.
After a grueling 17-hour coach journey, Zoe and Hari arrive in Inverness. Nina, heavily pregnant, drives them through fog to The Beeches, a towering gray stone house with turrets. Mrs. MacGlone shows them to a tiny attic room with iron beds and a rough blanket. Zoe finds no food, no hot water, and no phone signal.
The household is in disarray. Patrick, the five-year-old, bonds immediately with Hari, dubbing Zoe "Nanny Seven" because she is the seventh au pair. Mary, nine, is hostile and tells Zoe they do not want her there. Shackleton, 12, is withdrawn and glued to his computer. Both Mary and Shackleton have been excluded from school for violent incidents. Ramsay appears briefly, absurdly tall and distracted, telling Zoe to keep the children out of his library before retreating.
Nina's health deteriorates. The local GP diagnoses pre-eclampsia, a dangerous pregnancy complication, and Nina is hospitalized until her due date. Zoe must now run the book van alone while managing the children.
Slowly, Zoe transforms the household. She enforces chores, teaches Shackleton to cook, and establishes routines. Patrick becomes Hari's constant companion. When Hari nervously feeds toast to Porteous, a huge shaggy dog on the estate, he produces a small barking laugh, his first vocalization in a long time. Mary resists fiercely. During a laundry confrontation, Zoe nearly throws a hand-knitted fox cardigan into the fire, not realizing Mary's mother made it. Mary's devastation reveals the depth of her grief. Zoe also discovers Mary has been haunting the corridor at night to scare her away.
Struggling with Nina's regular village clientele, Zoe takes the van to the Loch Ness visitor center and stocks tourist-friendly titles. She befriends Murdo, a tour boat operator. Nina, from her hospital bed, accuses Zoe of turning the van into a tourist shop. Zoe also begins cataloguing rare books in Ramsay's library, which predates the house and once sheltered smuggled books during the Reformation. She sells items from the collection and uses the proceeds to negotiate household improvements.
When Zoe raises the topic of returning to school, Mary becomes agitated. Zoe finds the nine-year-old cutting her leg with a razor blade and notices an older scar beneath the fresh wound. The cut nicks an artery and could prove fatal. Ramsay refuses the doctors' recommendation for inpatient psychiatric care. Mary whispers to her father, "I miss her," and he breaks down, telling her he cannot lose another person. During her convalescence, Mary allows Zoe to read her stories about motherless girls, and Zoe decides to stop pretending the children's mother does not exist. On a shopping trip to Inverness, Mary quietly reveals her belief that her mother will come back for her.
At the village
Samhain festival, a Celtic autumn celebration on the estate grounds, Ramsay pulls Zoe into the dancing without recognizing her. When he realizes who she is, he drops her hand and apologizes. She flees, humiliated. Soon after, Larissa, a glamorous woman who has been pursuing Ramsay, arrives at The Beeches drunk, screaming that Ramsay is sleeping with the au pair. Mary screams that everyone lies to her and charges out. Ramsay ends his relationship with Larissa and returns to find Zoe sleeping outside Mary's door.
Jaz flies to Scotland with his new girlfriend, Shanti, proposing that Zoe return to London so he can share custody. Zoe is torn: Hari is thriving, but Jaz has a legal point. That night, Ramsay finds Zoe weeping in the kitchen; they share a quiet conversation about parenthood and loneliness but cannot act on the tension between them.
The crisis comes when Mary takes Hari outside at dawn and the two children end up adrift on the storm-lashed loch in an old rowing boat. Zoe calls Murdo, who launches immediately, and the village follows in a flotilla. Ramsay dives into freezing water to reach the children, who are found on a tiny strip of gravel shore. Hari speaks his first clear words: "Mummy. Ma sister she found me. We go boat," in a broad Scottish accent. Zoe is unsure what to make of Hari's claim that the "monster" pushed them to safety, whether he means a real creature or is simply confused.
At the hospital, Ramsay leads Zoe to a secure psychiatric facility and introduces her to Elspeth Urquart, the children's mother, a gaunt woman who shows no awareness of her surroundings. Elspeth had severe postnatal depression that escalated into addiction and erratic disappearances. Only Shackleton is biologically Ramsay's child; Mary and Patrick were fathered by other men during Elspeth's absences, but Ramsay raised them all. After Elspeth injured Mary, leaving the original scar, Ramsay obtained a restraining order. Elspeth then overdosed, stopped breathing for nine minutes, and sustained severe brain damage. Ramsay has been paying for her care, explaining why he is always away and short of money.
Jaz returns with Shanti and Surinder. Back in London, Shanti points out that Hari is thriving and that the flats Jaz found are inadequate. Jaz concedes and texts Zoe that she should stay. Ramsay asks Zoe to remain; she climbs into his lap and they both cry. Mary begins psychiatric sessions and starts medication. Zoe organizes a Halloween party at The Beeches that reconnects the children with the community, and during the celebration, she and Ramsay kiss in the woods.
That same night, Nina goes into labor. Zoe and Surinder rush her to the hospital in the book van. Nina's labor accelerates in the van, but they get her inside in time, and the baby, a boy named John, is born at midnight. The book business is resolved with a second van so Zoe can serve tourists while Nina returns to her village regulars.
Zoe and Ramsay begin a discreet relationship. Mrs. MacGlone silently acknowledges it by laying a fire and changing the bedding in a guest room. Mary returns to school, visits her mother after therapy sessions, and tells Zoe her mother likes to brush her hair. In the final scene, near Christmas, Jaz arrives with Shanti and his parents, who are meeting their grandchild for the first time. Zoe takes Hari's hand in one of hers and Patrick's in the other and steps forward, embracing the idea that families come in all shapes and sizes.