Ninjago: The Underground Society

It's been 10 years since Nya's brother Kai was kidnapped. And she's been searching for him despite the lack of clues to who or what took him from her. At the same time, Kai was been brought to an underground civilization. When they finally reunite...Can Nya save her brother and stop the invasion of Ninjago? Read to find out...
I don't own Ninjago...They belong to Cartoon Network and their creator.
I also don't own the picture used for the cover...it belongs to their creator.