We read this novel in gifted 4th grade, listening to audio tape, as mentioned before; I finished it ahead of everyone else and mispronounced "sadist" for several days until our teacher put it on our vocabulary list. In a nutshell: Meg, the protagonist, goes on a journey with her precocious brother Charles Wallace and schoolmate Calvin to rescue her father from another planet with the help of Ms. Whatsit, Ms. Who and Ms. Which, three strange ethereal beings.
First, the title "A Wrinkle in Time" refers to a new term called a tesseract, which is indeed such a wrinkle. The tesseract links the book together because the three "witches" in the story use the tesseract to travel through time and space, and a mishap with a tesseract starts the book by taking away Meg's father. Makes sense, no?
And since we're talking about Madeline L'Engle, may I say rest in peace, since she died in 2007, and thank you for writing such a wonderful book.