The story opens in an unnamed city, where Will Atenton, portrayed by Daniel Craig, decides to leave his successful career as an editor to dedicate himself to writing a book and spending quality time with his wife, Libby (Rachel Weisz), and their two daughters. Initially, their new life in a picturesque country home seems like the embodiment of the American dream. However, Will quickly senses an underlying tension that disrupts their tranquility, particularly between his neighbor, Anne Patterson (Naomi Watts), and her ex-husband, Jack, as he picks up their teenage daughter.
As Will settles into his new surroundings, he discovers a dark secret about the house they now call home—five years prior, the previous owner, Peter Ward, committed a horrific act, killing his wife and children. The tension escalates when Will's daughters start to report sightings of a mysterious man lurking near their windows at night. Driven by an urgent need to protect his family, Will investigates the murders, only to be met with resistance from the local police and an aloof Anne, who offers no insight into the unsettling history of the home.
Their inquiries lead them to uncover that Peter Ward had been released from custody due to a lack of evidence and is now residing in a halfway house, stirring public outrage. When Libby also encounters the enigmatic figure that the girls had mentioned, Will, suspecting it is Peter, becomes determined to confront him. Will's investigation takes him to the halfway house, where he mistakenly confronts a man named Martin Tishencko (Joe Pingue), instead of Ward.
In a deeply confounding twist, Will learns from staff at the psychiatric hospital that he is, in fact, Peter Ward, living under a false identity to escape the trauma of his family's death. As he struggles to accept this unsettling reality, he finds himself caught between two conflicting lives: one where he is a devoted husband and father, and another where he is a solitary man grappling with the guilt of his past.
Evicted from their now dilapidated home, Will seeks refuge with Anne, who provides care and support, believing in his innocence. However, tension mounts as Anne's ex-husband, Jack, confronts the situation, forcing Anne's daughter back home, prompting a chaotic chain of events that endangers everyone involved.
As Will battles his fractured reality, he revisits the memories of that tragic night, only to uncover a shocking revelation: the true murderer was Anne's hired assassin, Boyce, who mistakenly killed his family. The unfolding events lead to a terrifying climax where Will must confront not just his past, but the spectral figures of his wife and daughters who linger within his memories.
In a heart-wrenching finale, Will witnesses the ghosts of his loved ones aiding him in a desperate bid for survival against Jack and Boyce, clarifying the boundaries between life and death. The emotional weight of this moment compels Will to let go of his past. Ultimately, the film concludes with Will, now aware of his true identity as Peter Ward, gazing into a bookstore window at a book he authored about his harrowing experiences—a powerful testament to his journey, merging the lines between grief and recovery, and marking his renewal under the name he had long buried.
