Every circus tent contains a surprise, and every wild storm takes Harper closer to solving a fantastic mystery. Late one evening as the stars begin to twinkle, Harper and her friends are flying on her magic scarlet umbrella when they see a girl running on air. She leads them to the Circus of Dreams, a menagerie of wonders suspended in the sky. There, they meet the mesmerizing mermaid acrobat, the spectacular circus baker, and the mysterious fortune-teller, all more dazzling than even Harper could dream up. But as the friends learn about the Circus of Dreams, they discover an important secret about Harper's past that could change everything ...