A Wrinkle in Time is the story of Meg Murry, a teenage girl who is transported through time and space with her younger brother Charles Wallace and her friend Calvin O'Keefe. Their aim is to rescue her father, Mr. Murry, a gifted scientist, from the evil forces that hold him prisoner on another planet. Meg is a homely, loving girl dogged by personal insecurities and her concern for her father, who has been missing for over a year. The story takes off with the arrival of Mrs. Whatsit at the Murry house on a dark and stormy evening.
She looks like an eccentric tramp but is actually a celestial body with an ability to read Meg's thoughts. Mrs. Whatsit surprises Meg's mother by reassuring her of the existence of a tesseract -- a sort of "wrinkle" in space and time. It is through this wrinkle that Meg and her friends will travel through the fifth dimension in search of Mr. Murry.
A day after Mrs. Whatsit's visit, Meg and Charles Wallace go to Mrs. Whatsit's cabin in the afternoon. On the way, they meet Calvin O'Keefe, a popular boy in Meg's school whom Charles considers a kindred spirit. The trio learns from Mrs. Whatsit and her friends Mrs. Who and Mrs. Which that the universe is threatened by a great evil called the Dark Thing. It is taking the form of a giant cloud and swallowing the stars around it. Many planets have already fell victim to this evil force, including Camazotz -- the planet on which Mr. Murry is imprisoned.
The three Mrs. W's transport the children to Camazotz with instructions to them to always remain in each other's company while on their quest for Mr. Murry. When the children reach Camazotz, they see that all objects and places appear alike because the whole planet must conform to the rhythmic pulsation of IT, a giant disembodied brain. Little Charles Wallace tries to fight IT with his exceptional intelligence but is overpowered by the evil. He transforms into a robot-like creature uttering words with which IT infuses him. Charles leads Meg and Calvin to Mr. Murry and together they confront IT.
However, they, too, fail to withstand IT's power. They manage to escape only at the last minute, when Mr. Murry seizes Meg and Calvin, "tessering" away with them (traveling via another tesseract) to a gray planet called Ixchel. It is inhabited by tall, furry beasts who take good care of the travelers. Charles Wallace, however, remains possessed by IT, a prisoner of Camazotz. On planet Ixchel, three Mrs. W's appear once again, and Meg realizes that she must go back to Camazotz to rescue her brother. Mrs. Which tells Meg that she has one thing that IT does not have, and this will be her weapon against the evil. However, Meg must find this weapon for herself. Standing in front of IT, Meg realizes that it is her ability to love. Thus, by concentrating on her love for Charles, she is able to restore his true identity. Meg frees Charles from IT's clutches and tessers with him through time and space. They land in her twin brothers' vegetable garden on Earth and find that her father and Calvin are waiting for them. The whole family is happy to reunite. Mrs. W's pay a visit to them enroute their further travels.