"A Wind in the Door" is a science fiction novel by Madeleine L'Engle, part of the Time Quintet series. The story follows Meg Murry as she embarks on a journey to save her younger brother, Charles Wallace, who is gravely ill. With the help of her friend Calvin O'Keefe and a mysterious being named Proginoskes, they explore the concept of interconnectedness in the universe. The novel delves into themes of love, courage, and the battle between good and evil. It introduces the idea of farandolae, tiny life forms that play a crucial role in the balance of life, emphasizing the importance of every individual in the larger cosmic picture.