Mabel lives with her parents in the Mermaid Hotel, where she keeps an eye on all the guests, particularly her friend, the endlessly fascinating Madame Badobedah.

Madame Badobedah, who considers herself part of a long tradition of daring women such as Amelia Earhart and Zora Neale Hurston, has pirouetted through pyramids, swum with mermaids and helped a triceratops with a toothache. Just opening one of the drawers in her dressing table full of mementos elicits tales of banshees and curses and an exciting new quest – a reverse jewel heist!

On a mission to return a priceless 'borrowed' emerald, Mabel and her adopted godmother don their best spy costumes and head to the Natural History Museum, where they might just meet an old – very old – friend. But as Mabel discovers, no one is too young or old for adventure, because it’s adventuring that makes life worthwhile.