Cardiothoracic surgeon Steven Murphy leads a seemingly idyllic life with his wife Anna, an ophthalmologist, and their two children, Kim and Bob. Outside of his family, Steven has formed an unconventional friendship with Martin, a teenage boy with a troubled past whose father died in a surgery performed by Steven. As this friendship grows, Steven introduces Martin to his family, unaware of the unsettling impact this will have on their lives.

Despite the warm welcome, Martin's behavior grows increasingly sinister, foreshadowing a dark and inexplicable turn of events. Steven is faced with an impossible choice that threatens the very fabric of his family's existence, as Martin's actions reveal a vengeful motive. The family is plunged into a nightmarish situation that forces them to confront the fragility of their happiness and the lengths to which they must go to preserve it.