Siblings Jessie and Dwight are tasked with caring for their chronically ill younger brother, Thomas, who is unable to go outdoors during the day and relies on blood to survive. To meet his needs, the duo resorts to a dark lifestyle, routinely killing strangers—primarily homeless individuals and drifters—to provide Thomas with blood. Jessie, a waitress at a local diner, and Dwight, who spends his days pawning items he finds and visiting Pam (a prostitute he pays for brief conversations), struggle with the moral implications of their actions.
After a particularly gruesome murder, Dwight pleads with Jessie to seek legitimate medical help for Thomas, but she refuses and insists that he find another victim. In an attempt to follow her orders, Dwight tries to lure a Spanish-speaking migrant named Eduardo into his car. However, their confrontation takes a dangerous turn when Eduardo manages to escape and injures Dwight with a screwdriver. Although he manages to restrain Eduardo in a shed, this act of mercy complicates their already precarious situation.
When Dwight returns home without a fresh blood source, Jessie reacts violently by killing Pam, leaving Dwight shattered. That night, at the dinner table, Thomas expresses his loneliness and begs Jessie to let him interact with the local children he hears playing outside. Her rejection drives him to a breaking point, leading him to spill his bowl of blood in frustration. Eduardo seizes the opportunity to escape and confront Dwight, but this results in Dwight killing Eduardo in front of Thomas, who is left to process the horror.
The following day, in a desperate bid for connection, Thomas writes a note and tosses it outside to a group of teenagers, but Dwight intervenes just in time, causing Thomas to sustain severe burns in the process. One of the teens, Turner, finds Thomas' note and visits the house while Jessie is out hunting for a victim. Thomas attempts to connect through a guessing game about songs he's playing on the piano and even offers Turner blood to drink. Just as they begin to bond, Dwight catches them and, in a tense moment, prepares to let Turner leave until he hears Jessie returning with a new prey. In an effort to protect their secret, Dwight shoves Turner into a closet.
When Jessie discovers Turner and a struggle ensues, she is fatally stabbed. Despite her condition, she urges Thomas to take her blood. In the wake of the chaos, Dwight confronts Turner but ultimately lets him go, driving him home to his father, while he grapples with the horrifying scene he returns to—Jessie dead in the bathtub and Thomas drinking her blood.
In a face-off fueled by rage, Dwight locks Thomas away with the body of Jessie's last victim after burying Jessie and discarding the remaining blood. The next morning, Dwight informs Thomas of his decision to leave forever, yet a moment of clarity strikes as he witnesses a happy family at a diner, causing him to reconsider.
Back at home, Thomas, hiding under a blanket, expresses remorse for his part in Jessie's tragic fate, and the brothers share a heartfelt embrace. As they comfort one another, Thomas requests that Dwight remove the cardboard covering the window. Dwight complies, and as sunlight floods the room, they both weep.
Ultimately, with a heavy heart, Dwight sets off alone on a journey across the country, stopping at a jetty where he stares contemplatively over the water, burdened by loss yet seeking a path forward.
