Scarecrow of Oz
This book introduces a character that Baum previously wrote about in other books to Oz. Trot and Cap'n Bill start a day by rowing for a while in the bay near them. However, they manage to get into a whirlpool, and after a bad swim, make it to a hole. After a night's rest, the Ork also pops up in the hole and together, they journey through another hole in the back of the cave. They are able to escape death in the cavern by the wonderful talents of the Ork, and are then able to get to Oz.
You can buy this book through the Emerald City of Oz from the following publishers: