The Land of the Silver Apples by Nancy Farmer

Main Character: Jack, a Bard's apprentice
Location: England
Time period: 8th century
Genre: YA Fiction, Frantasy
Series: sequel to The Sea of Trolls

At the midwinter need-fire ceremony, Lucy disobeys the Bard and wears her silver necklace though metal is forbidden. This sets into motion a series of bad luck events which makes everyone cranky and disgruntled. Things come to a head when Giles reveals that Lucy is not really their child--he lost their child when the hobgoblins took her but found Lucy in the woods and took her home. So Jack now must go on a another quest, this time to the hobgoblin world and Elfland. He is accompanied by Pega, a slave girl he bought and freed, and joined by Torgill.

Jack and Thorgill are such engaging and likeble characters that I would not mind at all seeing more adventures with them.