Dr. Steven Murphy (Colin Farrell) is a renowned cardiovascular surgeon presiding over a spotless household with his ophthalmologist wife Anna (Nicole Kidman) and their two exemplary children, 12-year-old Bob (Sunny Suljic) and 14-year-old Kim (Raffey Cassidy). Lurking at the margins of his idyllic suburban existence is Martin (Barry Keoghan), a fatherless teen who Steven has covertly taken under his wing. As Martin begins insinuating himself into the family's life in ever-more unsettling displays, the full scope of his intent becomes menacingly clear when he confronts Steven with a long-forgotten transgression that will shatter the Murphy family's domestic bliss.