A Wrinkle in Time is the story of a sister and brother, Meg and Charles Wallace Murry, who rescue their father from captivity on the planet of Camazotz—and in the process save the universe from the clutches of an evil power called IT. They are aided in their struggles by Calvin O'Keefe, a friend who travels with them across the universe.

The novel introduces an entertaining cast of characters, many of whom exist only in the realm of the imagination.

Odd as some of these characters are— the three strange old ladies, Mrs. Who, Mrs. Whatsit, and Mrs. Which, who guide the children through the galaxies; the tentacled monster, Aunt Beast; and IT, a disembodied human brain—both the characters and the plot seem believable.

A Wrinkle in Time is much more than an intergalactic adventure story. L'Engle examines such issues as the nature of good and evil, the meaning of love, and the importance of self-sacrifice. She wishes to show readers what constitutes noble and admirable human behavior, yet her story is never a sermon. It is, instead, a chance for the reader to watch Meg, Calvin, and Charles Wallace face challenges, overcome them, and grow as a result of their tests.