When eleven-year-old Ann is sent to live with the famous Assassin Nuns of Pistachio, she expects nothing less than a life of swashbuckling adventures and covert rescue missions. Instead, she meets a group of mild-mannered women who prefer souffles to sword fighting and haven't stepped out of their mountaintop abbey in years. After Ann discovers that there's something very nasty going on in Pistachio, she decides it's time the nuns lived up to their reputation. Armed with wooden spoons, gardening gloves and a malfunctioning robot broom, can these unlikely heroes save the day?