Smith of Wootton Major
It takes place in a little town "not very long ago for those with long memories, not very far away fro those with long legs." The Master Cook of that village takes a vacation, and returns with an apprentice in tow. But something odd happens at the Feast of the Cake -- the cook stirs in a "fay-star" with little trinkets in the cake, and it's accidently swallowed by a boy there.
The boy (later called Smith) is changed by the fay-star, which sparkles on his forehead. When he grows up Smith ventures into Faery itself, and even meets the Faery Queen herself. The message she gives him is for her mysterious, missing husband, the King -- who turns out to be the last person anybody in Wootton Major would have expected.