A Wrinkle in Time — Madeleine L'engle

It was a dark and stormy night; Meg Murry, her small brother Charles Wallace, and her mother had come down to the kitchen for a midnight snack when they were upset by the arrival of a most disturbing stranger.

"Wild nights are my glory," the unearthly stranger told them. "I just got caught in a downdraft and blown off course. Let me sit down for a moment, and then I'll be on my way. Speaking of way, by the way, there is such a thing as a tesseract."

A tesseract (in case the reader doesn't know) is a wrinkle in time. To tell more would rob the reader of the enjoyment of Miss L'Engle's unusual book.