A Wrinkle in Time by 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 ways, by the way, there is such a thing as a tesseract."