On the edge of the dark sea of darkness (Wingfeather #1)

After living for years under the occupation by the evil Fangs of Dang, the Igiby children find a map rumoured to lead to the lost Jewels of Anniera – the one thing the Fangs will do anything to find. The family is thrown headlong into a perilous adventure, uncovering truths about who they are that will change their world forever.