There's only one passage between the Upper World and Droon -- the magical rainbow staircase. At least, that's what Eric and his friends have always believed. But now Ko and his beasts are attacking Zorfendorf Castle, a magical fortress that's hiding a huge secret: the Fifth River, another passage to the Upper World. Ko will do anything to get to the river -- and to the Upper World. And Eric, Julie, Neal, and Keeah will do anything to stop him!

作者簡介：

Tony Abbott is the author of more than thirty funny novels for young readers. Since childhood he has been drawn to stories that challenge the imagination, and, like Eric, Julie, and Neal, he often dreamed of finding doors that open to other worlds. Now that he is older, he thinks he may have discovered some of those doors. He calls them books.