The best babysitters are psyched to land their highest paying job yet - until they get to the house and realise they're babysitting Zelda Hooper, the meanest girl in school. And even though Zelda should be the one who's embarrassed that three girls her age are babysitting her, she finds ways to thwart them at every turn. But Zelda isn't the girls' only challenge. A new crop of French au pairs are stealing all their business - Quelle catastrophe! - forcing Dot to watch the rambunctious Morris boys, whose idea of a good time is lighting things on fire, while Bree teams up with Malia's pushy older sister to tackle a new pet cause: saving the salamanders of Playa del Mar. Will Malia, Dot, and Bree be able to handle their impossible new charges - or will this be the end of the Best Babysitters forever?