Stonekeeper's Curse

Emily and Navin's mother is still in a coma from the arachnopod's
poison, and there's only one place to find help: Kanalis, the bustling,
beautiful city of waterfalls. But when Em, her brother, and
Miskit and the rest of the robotic crew aboard the walking house
reach the city, they quickly realize that seeking help is looking
for trouble, dangerous trouble.