Katie is dreading the boring summer ahead while her best friends are all away at camp -- something that's way out of Katie and her mom's budget. But when Katie gets a job catsitting for her mysterious upstairs neighbor, life gets interesting. First, Madeline has 217 cats and they're not exactly normal cats. Also, why is Madeline always out exactly when the city's most notorious villain commits crimes? Is it possible that Katie's upstairs neighbor is really a super villain? Can Katie wrangle a whole lot of wayward cats, save a best friendship, and crack the biggest story in the city's history? Some heroes have capes ... Katie has cats.