Everyone remembers the smell of their grandmother's house. Everyone remembers the stories their grandmother told them. But does everyone remember their grandmother flirting with policemen? Driving illegally? Breaking into a zoo in the middle of the night? Firing a paintball gun from a balcony in her dressing gown? Seven-year-old Elsa does. Some might call Elsa's granny 'eccentric', or even 'crazy'. Elsa calls her a superhero. And granny's stories, of knights and princesses and dragons and castles, are her superpower. Because, as Elsa is starting to learn, heroes and villains don't always exist in imaginary kingdoms; they could live just down the hallway. As Christmas draws near, even the best superhero grandmothers may have one or two things they'd like to apologise for. And, in the process, Elsa can have some breath-taking adventures of her own ...