The Wingless Fairy Series, Book 4: Rebecca and the Missing Heir by Margaret Pearce

When baby Willyum is stolen by dwarf guards, Rebecca knows she has to act.

The dwarves believe George has betrayed their missing heir, Prince Lejon, and they won't return Willyum until Lejon is found. But Lejon has vanished, kidnapped and hidden far from the dwarf kingdom in a place no mortal has ever reached.

With her father George, her loyal goblin companions, and her brave white owl, Rebecca must journey through the dangerous underground hobgoblin waterways into Cantia, the land of ogres, trolls, and giants. There, locked in a tower guarded by monsters who don't believe in being vegetarian, Lejon waits.

But finding him is only part of the problem. Getting him out and getting home alive will take more than courage. It will take cleverness, loyalty, and a little help from unexpected friends.

Can one small girl outsmart ogres, escape hobgoblins, and save two lives before time runs out?