The green children of Woolpit

In the autumn of 1611, twelve-year-old Agnes is working in the fields to get the harvest all in when a strange sound leads her into the forest, where she discovers a boy and a girl trapped in a wolf pit, shouting in a strange tongue--and their skin is green. The other villagers think they are malnourished and came from a Flemish settlement--accounting for their strange skin color--but Agnes learns that they are actually of the a fair folk--fairies--and that she, too, has fairy blood in her. The fairy boy and girl convince Agnes to come underground with them to their kingdom, but she doesn't know that an ancient bargain has been struck to keep her there.