Reeling from the loss of her mother and father, teenage Maryann moves in with her grandparents, and is grateful when she manages to befriend Andy, a boy who uses a wheelchair. As Andy is very sick he must stay within his home per the instructions of his mother, Katherine, who also forbids him from having any visitors. When their visits are discovered, Andy's father, Richard, is initially fine with the visits, but Katherine is having none of it and her behavior grows increasingly erratic. After Katherine meets up with Maryann's grandparents, and reveals to them that Andy is dying, they prohibit her from visiting Andy again. However, Maryann's visits continue in Katherine's absence; she even takes Andy outside to play baseball. Their time together is cut short when Katherine calls her son to inform him she's on her way home. They manage to get back inside the house and Maryann hides in the basement, where she discovers a comatose boy. After Katherine discovers that Maryann visited her son, she verbally and physically assaults him. Richard comforts Andy, while Katherine takes care of Jason, the comatose boy. When Richard goes to get medical supplies, it is revealed he is having an affair. Katherine's behavior grows even more volatile, while Maryann discovers that Jason was abducted from the hospital as a baby. She sneaks back to Andy's house and discovers that a liver transplant will take place. Katherine and Richard operate on Andy, removing part of his liver. Richard later tells Andy that he had to have emergency surgery to remove his appendix. Meanwhile, Maryann returns to the house and informs Andy about the boy in the basement, and her suspicions that he was kidnapped. Andy, still skeptical, sneaks down to the basement and sees Jason. Richard spots him and tries to get him out before Katherine wakes up, but is unsuccessful. Andy pulls out the cords to Jason's machines, and Richard frantically tries to plug them in again. As Richard carries Andy out, Katherine divulges that Jason is her son. Maryann returns to the house again and Andy reveals to her that he is the real Jason, and that Jason is the real Andy. It is disclosed that the heart transplant, that is about to take place, is for the real Andy, Katherine and Richard's biological son. The pair had abducted the real Jason as a baby, so they could harvest his organs, and save their ill son. Maryann tries to help him escape, while Richard goes to retrieve him for surgery. Feeling remorseful for his actions, Richard helps him escape with Maryann. A frantic Katherine, refusing to accept that there is no hope for her son, subdues Richard with a sedative and pursues the children. A dazed Richard heads down to the basement, and, after unplugging his son's ventilator, sets the basement on fire and lies next to his son. Katherine, who had caught up to Jason and Maryann, is informed via her pager that her son's ventilator has been unplugged, and runs back to the house. She desperately tries to get her deceased son out of the burning house, but is unsuccessful when the roof collapses on them. In the end, Maryann and Jason, who has regained the use of his legs, are seen playing baseball.
Critical reception for The Harvest has been mostly positive. IndieWire, Variety, and Bloody Disgusting all gave favorable reviews for the film, and Bloody Disgusting heralded the film as "a triumphant return for one of indie cinema’s edgiest directors."
