Taken directly from Wikipedia.
A Wrinkle in Time (1962) is a science fantasy novel by Madeleine L’Engle. The book won a Newbery Medal, Sequoyah Book Award, and Lewis Carroll Shelf Award, and was runner-up for the Hans Christian Andersen Award. It is the first in L’Engle’s series of books about the Murry and O’Keefe families.
Meg Murry is a teenage girl, regarded by her classmates and teachers as a bad-tempered adolescent. Her family recognizes her problem as a lack of emotional maturity but also regards her as being capable of great things. The family includes her pretty scientist mother, her mysteriously missing scientist father, her five year-old brother Charles Wallace Murry — a nascent super-genius — and her 10-year-old twin brothers, the athletic Sandy and Dennys.
The book begins with the line, “It was a dark and stormy night,” an allusion to the opening words in Edward George Bulwer-Lytton’s 1830 novel Paul Clifford. During that stormy night the Murrys are visited by an eccentric old woman named Mrs. Whatsit, who has previously made the acquaintance of Charles Wallace. After drying her feet and having a snack with Charles, Meg and their mother, Mrs. Whatsit tells an already perplexed Dr. Murry that “there is such a thing as a tesseract,” which causes her to almost faint. It was a joke that Mr. and Mrs. Murry shared.
The next morning, Meg discovers the term refers to a scientific concept her father was working on before his mysterious disappearance. The following afternoon, Meg and Charles Wallace encounter Meg’s schoolmate, Calvin O’Keefe, a high-school junior who, although he is a “big man on campus”, considers himself a misfit as well. They go to visit an old haunted house near town which Charles Wallace already knows as the home of Mrs. Whatsit. There they encounter an eccentric companion of Mrs. Whatsit, a Mrs. Who. She promises that she and her friends will help Meg find and rescue her father. Meg tells Calvin a great deal about herself, including the disappearance of her father, and they become close. In the evening, Charles Wallace declares it is time for them to go on their mission to save their father. This is accompanied by the appearance of the third member of the “Mrs. Ws”, Mrs. Which.
Mrs. Whatsit, Mrs. Who, and Mrs. Which turn out to be angelic beings who transport Meg, Charles Wallace, and Calvin through the universe by means of tesseract, a fifth-dimensional phenomenon explained as being similar to folding the fabric of space and time. Their first stop is the planet Uriel, a Utopian planet filled with joyous beings who live always in a state of light and love. There the “Mrs W’s” reveal to the children that the universe is under attack from an evil being who appears as a large dark cloud called The Black Thing. Seeing the Black Thing even from a distance is disturbing to Meg. While working on a secret government project to achieve faster-than-light travel by tesseract, Meg’s father was accidentally trapped on Camazotz, an alien planet dominated by the “Black Thing”. The children are then taken elsewhere to visit a woman who is a kind of medium with a crystal ball. In it, they see that Earth is partially covered by the darkness, although great religious figures, philosophers, and artists have been fighting against it. Mrs Whatsit is revealed to be a former star who exploded in an act of self-sacrifice to fight the darkness.
The children travel to Camazotz to rescue Meg’s father. They find that all the inhabitants behave in a mechanistic way and seem to be all under the control of a single mind. They look for the central headquarters on the planet (described as CENTRAL Central Intelligence) and they discover a man with red eyes with telepathic abilities who can cast a hypnotic spell over their minds. He claims to know the whereabouts of their father. Charles Wallace looks into his eyes and becomes taken over by the mind controlling the planet. Under its influence, he takes Meg and Calvin to the place where Dr. Murry is being held prisoner because he would not succumb to the group mind. The planet turns out to be controlled by an evil disembodied brain with powerful telepathic abilities, which the inhabitants of Camazotz call “IT”. Charles Wallace takes them to the place where IT is held. In close proximity to IT, all of them are threatened by a possible telepathic takeover of their minds. Dr. Murray “tessers” in order to escape, but Charles Wallace is left behind, still mentally dominated by IT. The rest arrive on a dimly lit planet inhabited by sightless but wise creatures. Meg is almost paralyzed by an encounter with The Black Thing that occurred during the “tesser”. She feels frozen as if all energy and heat has been drained from her. Meg recovers over a period through the helpful care of Aunt Beast, and is tessered to Camazotz with Mrs. Whatsit, as she is the only one who can rescue Charles Wallace from IT. Confronting IT, Meg realizes that she can free her brother by loving him intensely, because love is an emotion that the evil IT cannot stand. Meg’s realization comes through her recalling a Biblical verse that “God has chosen the foolish things of this world to shame the wise and the weak things of the world to shame the strong.” Charles Wallace is freed, and the three Murrys and Calvin return home.
*** Reasons given include the book’s references to witches and crystal balls (although the characters are not in fact witches, and the crystal ball is a science fictional one), the claim that it “challenges religious beliefs”, and the listing of Jesus “with the names of great artists, philosophers, scientists, and religious leaders”. ***