Grace Stewart, portrayed by Nicole Kidman, is a devout Catholic mother residing in a secluded home on the island of Jersey, shortly after the tumult of World War II. She diligently cares for her two young children, Anne and Nicholas, who suffer from a rare condition known as Xeroderma Pigmentosa. This affliction makes them highly sensitive to sunlight, forcing their lives to revolve around strict rules to shield them from potential exposure to harmful rays.
The peace of their lives is disrupted with the arrival of three new staff members in the house: an elderly nanny named Mrs. Bertha Mills, an aged gardener, Mr. Edmund Tuttle, and a young mute girl, Lydia. However, strange occurrences soon plague the household, stirring Grace's suspicions that they may not be alone. Her daughter Anne begins to draw unsettling pictures of four mysterious figures—a man, a woman, a boy named Victor, and an elderly woman—claiming to have encountered them within the confines of their home. As the atmosphere thickens with tension, Grace hears the haunting melodies of a piano emanating from a locked room, where no one ought to be.
The chilling discovery of a "book of the dead," revealing 19th-century mourning portraits, adds to Grace's concerns as she discovers doors that should be closed standing ajar. In a desperate attempt to protect her family, Grace resorts to hunting for these supposed intruders with a shotgun, only to be confronted with inexplicable phenomena. Initially, she dismisses Anne's beliefs in ghosts, until she experiences the supernatural herself. Consumed by fear, she ventures out into the misty fog, seeking the local priest to bless their home.
Amidst this chaos, the servants seem to have their own agenda. Mrs. Mills engages with Anne, nurturing her grievances against her mother, while Mr. Tuttle digs an unmarked grave hidden beneath autumn leaves. In a twist of fate, Grace encounters her husband, Christopher Eccleston, whom she believed was lost in battle, leading to a day filled with strained silence and confusion. Grace's grief and irrational fears culminate in a series of events that pit her against an eerie old woman resembling her daughter.
As tensions rise, the story unfolds:
> "You are not my daughter!"
Grace's alarming discoveries escalate as her actions lead to fracturing her relationship with Anne. Despite Charles's return, trouble brews, as Anne reveals the terrifying realities of her mother’s behavior. The children’s visions intensify, and they find themselves drawing nearer to the veiled truth about their existence and the home they occupy. Eventually, they stumble upon the hidden graves corresponding to their enigmatic staff, paralleling Grace's gut-wrenching realization of the servants’ true identities.
Through chilling revelations, the narrative crystallizes when Anne and Nicholas learn that they, along with their mother, are trapped in a realm beyond life—ghosts haunting the shadows of their own demise after Grace's tragic descent into madness led her to unknowingly take her children's lives. As the fragments of memory emerge, Grace grapples with her fragmented reality, understanding their tragic circumstances and her husband’s oblivion of his own fate.
In the end, filled with the sorrow of regret, Grace and her children are comforted by Mrs. Mills, who explains their new life, emphasizing the need to coexist with the living while celebrating the newfound liberation from their sunlight afflictions. The family shares a poignant moment, embracing the warmth of sunshine that now envelops them freely as they watch Victor's family move away from their sanctuary.
