A Wrinkle in Time by Madeleine L’Engle begins a beautiful and fascinating fantasy series. Meg, 13, is brought into an otherworldly life by her younger brother, and is also accompanied by a friend and three female spirits. Her goal is to rescue her missing father, who is being held on another planet by an evil entity called It and It’s mindless subjects. She has to travel through a maze of time and space to do it. At one point, she is drawn into It’s hypnotic mind and almost loses herself, but is rescued by her companions.
Finally, Meg faces off with It to save her brother as well, and conquers it by revealing its one weakness – the inability to love (a somewhat sappy sounding premise, I realize, but actually common in Girls Underground stories).