Fairy Unicorns Islands in the Sky by Zanna Davidson
Zoe and Astra are on a quest to help the Unicorn King. This time, their adventures lead them high into the skies above Unicorn Island, in search of the Floating Islands. But someone is following them and the islands are not all that they seem. Will Zoe and Astra be able to complete the quest and help the King, or have they taken on more than they bargained for?