The Changeover: A Supernatural Romance

Blurb

The Changeover: a Supernatural Romance is a low fantasy novel for young adults by Margaret Mahy, published in 1984 by J. M. Dent in the U.K. It is set in Christchurch in the author's native New Zealand.
Mahy and The Changeover won the annual Carnegie Medal from the Library Association, recognising the year's best children's book by a British subject. Thus she became the fourth writer with two such honours, having won the 1982 Medal for The Haunting.
Atheneum Books published a U.S. edition within the year.
WorldCat reports that The Changeover is Mahy's novel most widely held in participating libraries, second among all her works behind a picture book collaboration, The Seven Chinese Brothers.