The Valley of the Lost

The Valley of the Lost is the seventh book in the Deltora Quest novel series written by Emily Rodda. The final gem from the Belt of Deltora, the diamond, is in the mysterious Valley of the Lost, held by the mysterious Guardian. To retrieve the gem, Lief, Barda, and Jasmine must play his game. If they win, they will get the gem. If they lose they will stay trapped inside the Valley of the Lost forever.