Michael Summer, a 911 dispatcher, leads a life alongside her husband, Ash, who is a doctor, and her mother, Anne Hartley. However, her life is interrupted by recurring nightmares featuring a threatening man trying to breach a door and visions of a young girl in a blue dress. One fateful day, Michael receives a silent 911 call from a child trapped in a burning building. Although she swiftly dispatches help, the address disappears from her system, leaving the police unable to find the location. Her supervisor informs her that there is no record of the call and advises her to take medical leave.
Meanwhile, Dr. Elaine Trussle, a colleague of Ash's, uncovers that Michael has a brain aneurysm. Unable to get in touch with Michael, Dr. Elaine alerts Ash, who is understandably concerned. As Michael’s nightmares begin to entwine with her waking life, she grows more convinced that they are connected to her stillborn daughter, Emma.
Leaving behind her cellphone, Michael is determined to trace the mysterious address from the 911 call, driven by clues from her visions of the girl in the blue dress. This quest leads her to the small town of Starlight. Ash, keeping tabs on her through credit card transactions, manages to find her and shares the grim news about her aneurysm. Yet, Michael is resolute in her belief that her experiences are not merely hallucinations; she feels the presence of the little girl, who guides her to a house with handprint stepping stones in the backyard. There, Michael learns that the girl in her visions is Carrie Waiverly, a six-year-old who mysteriously vanished thirty years earlier in 1978.
On meeting Carrie's parents, Henry and Silva Waiverly, Michael learns the tragic news that Carrie drowned in a nearby lake. However, the local newspaper editor, Bud Atherton, reveals a shocking truth: Carrie's body was never recovered. As Michael's investigation deepens, she experiences visions of another girl who died in a garage fire around the same time, still haunted by the menacing figure of Terrance Reed, the man from her dreams.
Driven by an emerging sense of purpose, Michael approaches Burton Hayes, an arsonist who is currently imprisoned. Hayes confesses to abducting Carrie and bringing her to the garage. Since no one found Carrie's body in the fire’s wreckage, Michael suspects that she might have escaped. Upon reviewing local hospital records from 1978, she discovers that a mute girl was admitted during that period, although her identity was never confirmed. The records also reveal that she was supposed to be transferred to St. Theresa's psychiatric facility, a decision opposed by her caseworker, who resigned in protest. To her shock, Michael learns that the caseworker was none other than her own mother, Anne Hartley.
Confronting her mother, Michael learns the heartbreaking truth: Anne couldn’t bear to let the girl go to an institution and instead raised her as her own. This revelation compels Michael to confront her buried memories, ultimately recognizing that Hayes was indeed the arsonist, while Reed courageously perished attempting to save her. Michael then remembers that Carrie had tried to communicate before the fire, unable to express that the other girl had already died.
After undergoing successful surgery for her aneurysm, Michael receives a touching gesture from Bud. He sends her a newspaper article chronicling her story along with a photograph of Reed in his Marine uniform. Bud's note reveals that Reed’s name has been cleared, and he has been posthumously recognized for his heroism.
Eventually, Michael reunites with her biological parents, revealing her true identity. Henry and Silva, at first hesitant, come to believe her once she recites a heartfelt bedtime prayer they once shared.
Fast forward a few years, and a moment of joy unfolds as Michael, Ash, Anne, and the Waiverly family gather at the Waiverly home, celebrating the birthday of Michael and Ash's new daughter. In a continuation of tradition, they create a new handprint stepping stone for the newest addition to the family, bringing the story full circle.