Plot
Momma and her two young children Nolan and Samuel "Sam" live in a cabin in a large forest. According to Momma, a supernatural force known as "The Evil" has spread across the world, leaving them the only survivors.
Momma is besieged by visions of supernatural entities that her sons cannot see but believe are real. The family spends their days foraging and hunting for food. To prevent the Evil from touching them, which Momma says ensures possession, the family must have ropes tied when they leave the house, connecting them back to the building. The boys must also chant a daily prayer to the house in thanks for it keeping them safe from the Evil.
While out foraging one day, Sam and Nolan get into an argument until Nolan intentionally steps on Sam's rope, causing Sam to fall, get disconnected from his rope, and break his ankle. Nolan unties himself to try and rescue Sam. The boys are rescued by Momma, who encounters the Evil in the shape of her mother. As Sam recovers from his fall, Nolan, who has started to doubt his mother's claims, questions him on what he saw but Sam dismisses his suspicions.
A brutal winter forces the family to use up a large amount of their stockpiled food, while preventing them from growing or hunting new food. Meanwhile, Momma's visions intensify, including the boys' father and her husband, whom she killed, along with her own mother and father as well as that of a mutilated Nolan. Sensing discontent from her sons, Momma tells them about her old life in the city and shows them an old Polaroid camera with one photo left.
Now fully out of food and forced to eat tree bark, Momma states that they need to kill and eat the family dog Kodda. Nolan protests, stating you shouldn't kill family, but Sam stands with Momma. When Momma takes Kodda into the greenhouse to kill him, Nolan cuts her rope and locks her inside, hoping she will see the Evil is not real. As Kodda runs away, Momma, encountering the Evil in her mother's form, kills herself, while Nolan prevents Sam from entering, distracting them both. When they find Momma dead, Nolan ties a rope to himself again. Sam blames Nolan for causing Momma's death, which Nolan feels guilty for, vowing to protect Sam from starving. As they continue to starve alone, Sam's behavior becomes more erratic and threatening.
Using the extra free rope from his mother, Nolan ventures further out and finds an empty road. Returning to the house, he encounters a hiker who has heard his calls for help. As the hiker grows increasingly concerned over Nolan's story and living conditions, Sam confronts him with a crossbow. Although Nolan and the hiker try to de-escalate the situation, Sam shoots the hiker. Nolan follows the wounded hiker as he calls 911 and dies, then retrieves his backpack filled with food. That night, a young girl, claiming to be the hiker's daughter, arrives at the house and confronts Sam. Noticing that Sam has her father's flashlight, she flees as he chases after her, shouting that it was an accident. When Sam unties himself to reach her, the girl reveals herself to be the Evil and manages to touch Sam.
Back at the house, Sam, now seemingly possessed and exhibiting erratic behavior, tries to kill Nolan. Sam sets the house on fire as Nolan is confronted by the Evil in the form of Momma. Nolan drags Momma into a small crawlspace in the house that gives shelter to the pair of them from the fire. The Evil sheds Momma's skin to reveal a scaled creature that dissipates as the two hug each other. The fire burns the house down and Sam takes the last photo with the Polaroid. Paramedics arrive and retrieve Nolan from the remains of the house. As he is flown away, Kodda running after them on the street below, Nolan asks where Sam is and sees that he too has been rescued. The helicopter reaches civilization, revealing that Momma had been lying about the rest of the world. The Evil is revealed to be an allegory for mental illness.
