In a time when the Industrial Revolution has escalated into all-out warfare, mad science rules the world... with mixed success.
With the help of Krosp, Emperor of All Cats, Agatha has escaped from the massive airship known as Castle Wulfenbach. After crashing their escape dirigible, Agatha and Krosp fall in with Master Payne's Circus of Adventure, a traveling troupe of performers dedicated to staging Heterodyne shows—dramatizations of the exploits of Bill and Barry Heterodyne and their allies—who are unaware of Agatha's connection to the Heterodyne line.
Pursued by the ruthless Baron Klaus Wulfenbach, his handsome son Gil, and their minions (not to mention Othar Tryggvassen, Gentleman Adventurer), Agatha hides in plain sight among the circus folk, servicing their clanks and proving herself adept in performing the role of Lucrezia Mongfish, nemesis to—and later wife of—Bill Heterodyne. She also begins training under Zeetha, swordmistress and princess of the lost city of Skifander. Together, Agatha, Krosp, and the performers travel across the treacherous wasteland of war-torn Europa, towards Mechanicsburg, and the ancestral home of the Heterodynes—Castle Heterodyne.
But with many perils standing in her way—including Wulfenbach's crack troops, mysterious Geisterdamen, savage Jagermonsters, and the fabled Storm King—it's going to take more than a spark of Mad Science for Agatha to get through.