Hugo not only survived his summer travels with Alustin but stories of their accomplishments preceded them home to Skyhold. Thus, his fellow students have now dubbed Hugo "Stormward". Alustin is being cagey about the purpose of that trip but Sabae suspects that he used her and her fellow students as a cover to spy on the dragon Idris. There is no doubt that Alustin has been a remarkable help to Sabae, helping her make the most of her strange magic, so she is keeping her distrust to herself for now. Her doubts only grow when they get home and the four friends are tasked with ferreting out a traitor on the Skyhold Council. Kanderon has known for years that someone on the Council has been working against her but she was angered when the traitor made sure a vote to protect Hugo from Bakori, the demon in the labyrinth below Skyhold, went against Kanderon. The Council claims to believe Kanderon is exaggerating the danger to ensure an easy test for her "Pact"ed student, but she is certain this is a direct attack against Hugo because of their Pact. Hugo and his friends are uncertain how much help they can be, but except for Sabae, they trust Alustin and Kanderon implicitly.
While the second book in the series dropped several hints of a deeper story behind the "friends at a magic academy" trope, this third book finally starts to delve deeper into the world and story arc on several levels. Hugo is in a couple of classes that give us deeper insight into the magic system, which has a solid structure but still allows a limitless variety of ways for mages to manifest power. Dealing with members of the council brings up the concept of Archmages who are all mages strong enough to be considered lesser powers. To be considered an "Archmage" a mage must not only have power but also push further and be innovative. One of the Councilors is an Archmage with an affinity for ceramics. In battle he summons armor of hexagonal ceramic tiles and also uses them offensively. Rumor has it he has a layer of tiny tiles under his skin as well. I can't think of another series that thinks up ways to battle magically with paper, ceramics, and silk along with the more common elements. And the good news is that there are definitely plenty of battles in this series!
The political situation is also taking shape. Kanderon is a Great Power who's primary rivals around the Erg Desert are Sabae's storm mage grandmother and the dragon queen Idris. In this multiverse many Great Powers travel between worlds using the labyrinths, so the politics of Hugo's world are being manipulated by organizations with ties to many worlds. So far our foursome of friends has only gotten superficial hints at what those factions might want. One big question is, why are they so interested in this particular world? Another is, where do Kanderon and the other powers fit in? Most important at the moment though, who does the traitor really work for and why do they have it out for Hugo?
Each book in this series seems deeper and more interesting than the last.