A Wind in the Door (by Madeleine L'Engle)

Then she sees the fantastic creature, actually a "singular cherubim." It has been sent by a wise, humanlike Teacher to help Meg in a quest to heal Charles Wallace. Also accompanying her will be her friend, Calvin O'Keefe, and her archenemy, Mr. Jenkins, the dour principal of Charles Wallace's school.

The travelers journey from a faraway galaxy to inside Charles Wallace's body, where a cosmic battle is taking place. By kything--communicating without words--and learning the importance of Naming (loving) her enemies, Meg saves her brother with the help of both Calvin and the surprisingly lovable Mr. Jenkins.

This is the second of Madeleine L'Engle's Chronos Quartet novels featuring the Murry family and their journeys through time and space. With believable characters and a suspenseful plot, it is arguably the best of the sequels to the classic A Wrinkle in Time. In some books in the Quartet, the hypersensitive, loving, and gifted Murry children speak and act like people much older or younger than their given years. Here they face enough real-kid problems, such as Charles Wallace's torment at the hands of school bullies, to seem real.

The three trials Meg must pass are interpersonal; her ability to communicate love is tested. Some scenes are long on dialogue and short on action; "too many talky scenes" was one 12-year-old's only negative comment. Yet there are enough surprises to sustain the suspense, and the ideas that drive the scenes are interesting. This is a rewarding book with generous helpings of the L'Engle magic.