The film opens on a frail man, Bud (David Pendleton), who is visibly suffering, gasping for breath while covered in painful boils. His daughter Sarah (Carmen Ejogo) tenderly speaks to him, wearing a gas mask, soothingly assuring him that everything will be alright. Shortly thereafter, Sarah's husband Paul (Joel Edgerton) and their son Travis (Kelvin Harrison Jr.) transport Bud into the woods. In a somber act of mercy, Travis places a pillow over his grandfather’s head and shoots him. Bud's body is unceremoniously deposited into an open grave, soaked in lighter fluid, and set ablaze.
The family's lifestyle is insular, with the trio—along with their dog, Stanley—cut off from the outside world, as it is heavily suggested that a deadly virus has ravaged the country, leaving them in a haunting state of isolation. Travis often finds himself plagued by nightmares, seeing visions of that same sick man from earlier in the house, wheezing and in distress on the bed. Each night, these visions lead him to wake up frightened, as his parents become aware of a potential intruder at their door.
When ominous banging is heard, Paul and Sarah arm themselves and confront the threat. They soon discover it is Will (Christopher Abbott), who, after being ordered to drop his weapon, is knocked unconscious by Paul. Tied to a tree with a sack over his head, Will’s muffled cries resonate in the eerie silence of the woods, inspiring yet another terrifying dream for Travis—who sees Will with shadowy, menacing eyes staring at him.
After a day, Paul approaches Will, removes the sack, and offers him water in exchange for answers. Will explains that he mistook their house for abandoned and was merely seeking resources for his wife and child, several miles away. He mentions a desolate 80-mile stretch devoid of any life, and even proposes a barter—goats and chickens for assistance. Trusting Will, Paul provides him water.
Prompted by concern, Paul drives Will to help him find his family. However, their journey becomes perilous when shots ring out, forcing Paul to act. After confronting two men in the woods, Paul’s aggression leads to their demise. Will had intended to spare one for information, highlighting the fragility of their existence in this harsh reality.
Eventually, they return home with Will’s wife, Kim (Riley Keough), and their young son, Andrew (Griffin Robert Faulkner). Welcoming them in, Paul and Sarah establish boundaries to prevent conflict. Slowly, both families coexist, sharing meals and games—a delicate balance forged in immediate survival.
Amidst the backdrop of this struggle, Travis finds himself intrigued by Kim, culminating in strange dreams where she blurs the lines between comfort and horror. One evening, as they converse over shared discontent, Kim expresses a wish for sweet treats—a reminder of their lost normalcy.
The tranquility shatters when Stanley begins barking frantically, following an unsettling turn of events. Travis chases after the dog into the depths of the woods, only to face Paul’s ire for straying off. The situation worsens when Travis discovers Andrew alone, and eerie thumping reverberates through the house. Tragically, they find Stanley badly injured, leading Paul to take the heartbreaking decision to euthanize him, with Travis hearing the gunshot echo like a death knell.
An unsettling tension rises as both families navigate the emotional fallout. Suspicion grows, especially as Travis’s innocent guidance of Andrew raises questions about their health. As their tenuous relationships deteriorate, even more horror ensues—Travis is deeply haunted by a terrifying visage of Bud in nightmarish fever dreams.
The following morning, troubling signs from Andrew prompt Paul to check on his new neighbors. When Will refuses to comply, a standoff ensues, leading to chaos that results in tragedy for both families. In a series of desperate actions, Paul inadvertently kills Andrew amidst the chaos, with Kim screaming in anguish, demanding Paul take her life as well.
The emotional weight becomes unbearable as Travis succumbs to the virus. Sarah desperately tries to comfort him as he spirals down into illness. As he crosses the threshold from life to death, his parents share a moment of poignant sorrow, left alone in their hauntingly silent home.
Finally, the chilling conclusion rests upon Paul and Sarah, now infected, silently sharing a devastated gaze at the table, the weight of their reality crashing down as the screen fades to black—leaving the audience to grapple with the catastrophic ramifications of their choices in a world stripped bare of humanity.
