Late one evening as the stars begin to twinkle, Harper and her friends are flying on the scarlet umbrella when they see a girl running on air, skipping along a tightrope. She leads them to the Circus of Dreams, suspended in the air by hot air balloons.

As the children meet the mermaid acrobat, the spectacular circus baker, the mysterious fortune teller and the acrobatics troop, they begin to realise something about Harper's past...