After visiting the castle in Scotland which her family has inherited and returning home to Canada, twelve-year-old Emily finds that she has accidentally brought back with her a boggart, an invisible and mischievous spirit with a fondness for practical jokes.
Susan Mary Cooper (born 1935) is an English-born American author of children's books. She is best known for The Dark Is Rising, a five-volume contemporary fantasy series set in England and Wales, which incorporates British mythology, such as the Arthurian legends, and Welsh folk heroes. For that work, she won in 2012 the lifetime Margaret A. Edwards Award, which the American Library Association annually confers upon an author and specified writings for "significant and lasting contribution to young adult literature".
Susan Cooper. Wikipedia.