In a suburb of Detroit, Michigan, during the mid 2010s, Malorie lives in a house with two four-year-old children whom she refers to simply as the Boy and the Girl. Four years earlier, a mysterious problem spread through the world: After seeing an unknown entity or creature, people started to act irrationally and committed acts of violence, including murder and suicide; only a few managed to survive. To protect herself and the children from seeing these creatures, Malorie keeps the windows of the house always covered and wears a blindfold whenever she goes outside. She also keeps microphones in the yard connected to amplifiers in the house and trains the children to listen closely. The house is dirty, including bloodstains that Malorie tried to wash out of the carpet.

Sensing fog in the air, Malorie decides the time is right for her and the children to leave the house and take a risky 20-mile trip down the nearby river. She wakes the children and tells them to put on their blindfolds and dress warmly. Before leaving, she commits the Boy and the Girl to follow her instructions, keep their blindfolds on, and listen carefully throughout their journey.