Sky raiders Five kingdoms

I recently finished reading Sky raiders Five kingdoms by Brandon Mull. Its about this boy from earth and his friends getting sucked into another world - planet. They have a tremendous adventure. I don't want to spoil the surprise but here is some of it. The boy's name is Cole. He wanted to save his Friends. They became slaves. Cole tried to save them but he got Caught to. He was sold to a man who worked with the Sky Raiders. They were a group of people who raided clouds that had castles on them. Sometimes the castles were dangerous sometimes they were safe. The raiders wanted to get gold and valuables from the castles. Then they would sell the goods for food and money. Cole and some of his friends escaped and became free. This was a summary of some of the book. Brandon Mull is a good writer.