Twin brothers Elias and Lukas return home to live with their estranged mother, a former actress, after staying with their father since their divorce. Upon seeing her again, they are disturbed to find her wearing a full bandage over her whole head, resembling a white balaclava. Mother (who is never given a name) explains she has had cosmetic surgery. She gives the boys some house rules, which include not entering her room or the barn outside. While playing outside in the field, the boys discover the barn. Exploring inside, Elias finds old toys of theirs. Mother discovers they've been in the barn and chastises them, proclaiming that from then on they will stay indoors.The boys quickly sense something strange about Mother, who does not seem interested in reconnecting with them; she drinks heavily, appears angry, and will not sing the lullaby she always used to sing to them as children. Elias also discovers Mother has thrown away a drawing he made of the three of them, which upsets him. During the night, Elias overhears Mother talking on the phone; she says she cannot go on pretending and wants him gone.After seeing an old headshot of Mother with green eyes, who now has blue eyes, the boys begin to question whether the woman they are living with is really their mother. When they attempt to contact their father, Mother breaks their shared cell phone. One night while she is taking a bath, Elias attempts to remove the skincare face mask she is wearing; an argument ensues and, after Elias tells her she is not their mother, she slaps him, then sprays him with freezing cold shower water until he admits he is wrong.Terrified of Mother, the boys leave in the middle of the night and attempt to seek help from a nearby house, which they discover is abandoned. They break in to spend the night but are found by two local state troopers who take them back to Mother's house. Mother, who has now removed her bandage, insists they are imagining things and says to police that Elias injured his lip from slipping near the pool.The following morning, Mother wakes to find her arms and legs tied to the bed with duct tape. She demands to be let free, adamant she is their mother. She explains she wore green contact lenses as an actress, claiming they are downstairs in her purse. Lukas tells Elias he searched the purse and did not find them. Elias suddenly feels uneasy about leaving Mother tied up and in pain, but Lukas persuades him to go, branding her a liar. While waiting for a taxi nearby, Elias returns to the house, claiming he forgot to pack his toothbrush. He looks in Mother's purse and finds the contact lenses. Lukas appears and begs Elias to let him explain. Elias flees to the bedroom to free Mother while Lukas disappears.Mother takes Elias to the barn and shows him a bullet hole in one of the walls that is covered in blood. Upon seeing it, Elias breaks down; it is revealed Elias accidentally shot and killed Lukas, meaning Lukas has been a hallucination the entire time. His death sent Mother into a grief-stricken depression, resulting in her divorce and estrangement from Elias. Mother attempts to console him, but in a confused rage, he lashes out and pushes Mother from the barn loft; her lantern smashes in the process, resulting in a fire. Elias flees and tearfully watches the barn burn to the ground. Elias has a hallucination of Mother and Lukas who appear at his side. With a smile, Mother tells him he has done nothing wrong, and they embrace. (thanks to Wikipedia)