Isaac is a young child living with his deeply religious mother in a small house on a hill. One day, his mother hears what she believes to be the voice of God, telling her that Isaac has been corrupted by sin and must be saved. She strips him of his possessions, locks him in his room, and eventually receives a command to sacrifice her son as proof of her devotion. Facing death at his mother's hands, Isaac discovers a trap door in his bedroom floor and escapes into the basement below. There, he must fight his way through dark and twisted dungeons filled with monsters, with only his tears as a weapon, hoping to survive whatever lies deeper beneath.