Trot and Cap'n Bill

Young Trot and the old captain, peg-legged Cap'n Bill, might seem like odd friends, but they are constant companions and Cap'n Bill taught her to love and appreciate the ocean. Trot was especially fascinated by the idea of mermaids and talked about them often with Cap'n Bill, who warned that no one who had met a mermaid had ever lived to tell the tale. One day while out sailing around, the pair is greeted by a beautiful mermaid who extends an invitation for them to come and visit their underwater kingdom and even become mermaids themselves for the adventure.

After an explanation of how the magic umbrella works, the two children, joined by Cap'n Bill, decide to take a trip to a nearby island. They call it "Sky Island" because it looks like it's "halfway in the sky"—but the umbrella takes them to a different place entirely, a literal island in the sky.

L. Frank Baum called this and The Wizard of Oz his two best books! A magic umbrella transports Trot, Buttonbright, and Cap'n Bill to an island in the sky inhabited by the Blues, the Pinks, and the evil Boolooroo.