Mirabelle and Meg Moffat are twins, and their mom and dad are famous circus acrobats. Mirabelle is fearless. She promises to be the most topsy-turvy, upside-down acrobat of all. Unlike Meg, who is afraid of heights. But with a grand new show featuring Mirabelle about to open, it soon becomes clear that there is at least one thing that does scare Mirabelle. Could it be time for Meg's talent to shine?