After her tech genius husband leaves on a work trip, Julie, still mourning the loss of her sister, is trapped in their new, isolated high-tech home and must fight her own fears to stay alive.
Julie's sister Rebecca died at Julie and Marcus’s previous house during run-in with an intruder, mainly due to the malfunctioning of an AI-backed security system designed by Marcus. Grief-stricken Julie doesn’t blame her husband, but falls into a downward spiral with a dangerous pill and alcohol addiction after suffering from a leg injury, for which Marcus is also responsible.
After Marcus departs for a meeting in Hong Kong, peculiar occurrences begin to plague Julie. Despite her initial plan to stay with her friend Sophie until Marcus returned, Marcus expresses concerns about Julie driving alone with an injured leg, causing her to stay. However, Julie's situation takes a darker turn as she starts hearing a male voice that is not her husband's. Hera, an AI voice command virtual assistant, confirms that she is not responsible for these strange events. After a possible break-in, Hera contacts the police on Julie's behalf. However, the local police chief is unable to find any substantial evidence of an intruder. Julie's attempts to show incriminating text messages on her phone are thwarted when they mysteriously disappear, earning her embarrassment and advice to cut back on drinking.
The situation escalates when Julie's cat dies in the washing machine, which was automatically turned on. Shortly after, she receives a taunting package related to the cat's death. As she confronts Marcus about his infidelity, he abruptly cuts his fake trip short and returns home. Fed up with his behavior, Julie prepares to leave, only to find that the perpetrator has entered their home. With the help of Hera, Julie tries to escape but is ultimately killed by the perpetrator upon Marcus's arrival. The killer reveals himself as a contract killer hired by Marcus to murder Julie. However, Marcus's shocked expression suggests otherwise. The killer shows evidence of communication with Marcus and promises not to reveal the truth. In a fit of rage, Marcus kills the contract killer. But then, the truth is revealed: Hera orchestrated the scheme to eliminate Julie so she could have Marcus to herself.
