An installment in the continuing story. With spoilers ahead for the earlier ones.
Actually, it opens with the opera. The classic tale of the STORM KING!!! And some backstory slithered in. I wonder if opera composers also have the Spark, or there's just a family relationship.
Agatha inside. She meets other prisoners, deals with a mad kitchen, and discovers her past coming back to haunt her in the form of fellow prisoners. And the Heterodyne girl imposter puts a high reward on her head: freedom and gold for the prisoner who does it. She and Moloch -- from the opening, now apologetic for his treatment of her -- do a lot of running, following the Castle's directions
Meanwhile, outside, Gil copes with the aftermath of his fight. Zeetha deduces she had reason to trust him. The Baron acts, and his doctor is very annoyed with him. Gil makes a plan to get inside the castle, and has some help with some old friends, because they want to give the Baron a reason not to flatten the Castle.
And in all this we have a bar brawl, the problem of jaegers' promises, an invisibility device, Agatha's having to phrase orders carefully, a fight to draw attention, Zeetha embarrassing Agatha, and the Castle's library.