After escaping from the massive airship known as Castle Wulfenbach, Agatha falls in with a travelling troupe of performers, where she begins training under Zeetha, swordmistress and princess of the lost city of Skifander. With Wulfenbach on her trail, it's going to take more than a spark of Mad Science for Agatha to traverse the treacherous wasteland of war-torn Europa.

Agatha Heterodyne is the last heir to the Maddest of Mad Scientist families, and now she's returning to her ancestral home, the warped little town of Mechanicsburg, to claim her inheritance. Unfortunately, it turns out that she's not the only one with that idea in mind. When an impostor claiming to be the rightful heir appears, Agatha must convince the artificial intelligence that animates her family's castle that she is, in fact, the new Heterodyne. But as Agatha soon discovers, this will be no simple task, as the Castle itself is completely insane.