Dr. Rue Siebert is one of the novel’s protagonists. A talented chemical engineer at Kline, she is very close to her boss and mentor, Florence, and her best friend, Tisha, who also works at Kline. Rue is serious and socially awkward; Florence and Tisha are her only real friends. Because of her perceived social ineptitude, she prefers to have one-time sexual encounters with men rather than building lasting relationships. Part of her reluctance to form relationships with people stems from her traumatic childhood. Her father left her family when she and her younger brother, Vincent, were very young, and they were forced to depend on their neglectful mother and often went hungry. Her romance with Eli Killgore allows her to grow as a person and build more meaningful relationships with others, making her a dynamic character.

As an adult, Rue has a strained relationship with her brother, partly because she feels guilty for leaving him with their mother when she went to college. The food scarcity that Rue and Vincent experienced as children has left her with anxiety and a disordered relationship with food, but it has also driven her to develop a microbial coating that can extend the shelf life of food.