In the heart of Moscow, mute American make-up artist Billy Hughes finds herself working on a low-budget horror film. One night, after the crew wraps up and leaves, Billy realizes she has forgotten a piece of equipment and returns alone to the soundstage. There, she witnesses what seems to be the filming of a brutal scene, but it quickly becomes apparent that it's not an act – she has stumbled upon the murder of a woman. Terrified and unable to scream for help, Billy narrowly escapes detection by the killers and rushes to recount her harrowing experience to the film's crew and her sister, Karen. However, her claims are met with skepticism.

As Billy tries to convince others of what she saw, she becomes ensnared in a deadly game of cat and mouse with the murderers. They soon learn of her presence during the murder, and determined to silence her, they pursue her through the perilous streets of Moscow. Desperate to find someone who believes her before she becomes their next victim, Billy's quest for safety spirals into a tension-filled chase that reveals deeper criminal underpinnings. In a race against time, her struggle to stay alive grows increasingly precarious as these enigmatic killers close in on their mute witness.