An installment in the continuing story. With spoilers ahead for the earlier ones.
First page is their Hugo acceptance speech, with Agatha interrupting to figure out the cause. It's not mind-control worms.
It opens easily enough, with guards watching over the rejoicing in Mechanicsburg. The Baron had sent not soldiers but barrels of strong drink. But within a page, we are following a new arrival, which culminates in Othar's being sent into the Castle to retrieve Gil.
Meanwhile in the Castle, Gil bumps into the false Heterodyne heir. Turns out she's Zola, someone he knew in Paris -- where she had a dreadful habit of getting mixed up with things that he had to rescue her from. And Agatha discovers that she built a death ray in her sleep, and that Tarvek is seriously ill. She decides to recruit Gil to help.
They meet up, a fraught moment interrupted by Dr. Merlot, out for revenge. A bit of an adventure, revealing why he blames Agatha for his presence there.
The first of many revelations and much action during the course of a heroic effort to cure Tarvek. Several rescues of Zola. Tarvek's revealing how he and Gil had known each other as boys. The realization that most of the medicinal stuff in the castle is old. A big fight between Gil and Tarvek that does what they want it to, and a secret, quiet bargain between them.
This one doesn't end on a mere transition. For the first time, it ends on a cliff-hanger.