In a world ravaged by an unspecified contagion, a family of three, Paul, his wife Sarah, and their teenage son Travis, reside in a desolate home deep within the woods. They have established strict sanitary protocols and security measures to protect themselves against the illness and any potential threats. The family lives in a state of constant vigilance and paranoia, which is intensified by the nightmares that haunt Travis, who is also struggling with the loss of his grandfather to the mysterious disease.

Their lives take a turn when an intruder, Will, attempts to break into their home. After subduing and interrogating him, they learn that he has a wife and child, and is scouring for supplies and shelter. Sympathizing with his plight, the family debates and ultimately decides to extend an offer to share their home with Will's family, in hopes of mutual benefit and increased security. This decision results in a precarious alliance, with both families attempting to coexist despite the omnipresent fear and mistrust that the outside world and the threat of infection breed among them.