It has science-fiction; The Drs. Murray, parents of Meg, Charles Wallace and the twins) are scientists who are researching Time and Space. Dr. Murray takes a time trip and so do the kids.
There is also magic; a trio of "witches" shows up--Mrs. Whatsit, Mrs. Who and Mrs. Which, and they take Meg, her brother Charles-Wallace, and their new friend Calvin on an epic adventure.
It's also the story of a family with a deep trouble who nonetheless stay together, the story of a young girl who is just coming into adolescence with all the awkwardness and confusing feelings, and the story of a special little boy who is thought to be retarded by townspeople.