The sixth volume of Girl Genius opens aboard Castle Wulfenbach, where Klaus Wulfenbach discusses his suspicions of Agatha with Bangladesh DuPree. It chronicles Agatha's attempts to escape from the mind control of Lucrezia Mongfish, and ends with a climactic battle with Wulfenbach forces after Lucrezia accidentally solves the problem by putting on Agatha's locket, (the golden trilobite of the title). There are fights with Geisterdamen, Jägermonsters, green glowy things and sewer monsters, as well as breathtakingly backbiting machinations between the Sturmvoraus family members. Princess Anevka has her own unasked question answered in a very final manner.
Who can you trust? That's the question that permeates this volume, as each of the characters seeking to control Agatha have their own agendas, and aren't even revealing them to the reader. The one question that is definitely answered is "What is a battle circus?"
The colors were done by Cheyenne Wright.
This volume contains the single-page short short story "An Agatha Heterodyne 1 Minute Mystery."