Humans on Earth are increasingly suffering from nightmares. David meets a caterpillar named Houdin, who is really an enchanted wizard from Remin, a world where dreams are, well, processed. "It's hard to explain but that's the best I can do right now," Houdin tells David. So you'll just have to be satisfied with that.
Anyway ... David and Houdin travel to Remin, sort of through a bathtub drain, but it's hard to tell. There David learns that an evil wizard named Thane has stolen the Imaginator (for reasons never entirely clear, but that seem to have something to do with teaching everyone a lesson, only then he goes insane, of course, which can explain anything), which controls spectrum, which ... oh, never mind, anyway, he's bad and has to be defeated. And, of course, only David can do it.