Gilbert Morris 
Victims of Nimbo [EPUB ebook] 

The Cloud People need the Seven Sleepers’ help, but the boys are gone on a hunting trip. Sarah and Abby decide not to wait for them. Maybe they can solve the problem all by themselves. Big mistake. What they can’t see coming is trouble with an evil high priest who will put Sarah’s life in danger. But their wise friend Goel knows how to bring good things out of bad — even when his people make foolish choices.