Premise
The Empire of Khanum is surrounded by a sea wall. Each wet season, leviathans emerge from the deep ocean and are turned back by imperial weaponry. Imperial citizens live in constant fear of a breach in the walls.
The administrative branch of the Empire includes divisions called Iyalets; these include the Iudex (investigators), Legion (armed forces), Engineers (infrastructure), and Apothetikals (botanical modification). Apothetikals use leviathan-derived technology to modify both plants and humans, giving them special powers. Humans who have received apothetikal modifications are called sublimes. Several types of sublimes include engravers (who have perfect memory), axioms (who have augmented mathematical abilities), and cracklers (who have enhanced physical strength).
The Empire is divided into various cantons. Years before the start of the story, the canton of Oypat was overrun by a modified plant known as dappleglass. Despite the efforts of the apothetikals, no cure for dappleglass infestation was found. The entire canton was sealed off, and its citizens were evacuated to other regions.
Plot
Dinios "Din" Kol, a young engraver, is chosen as the assistant to the eccentric Iudex investigator Anagosa "Ana" Dolabra. Din is sent to investigate the murder of engineer Taqtasa Blas, whose body is found in a mansion owned by the wealthy Haza family. Blas was poisoned with dappleglass, which caused plant matter to grow instantaneously through his body. Soon, a leviathan breaches the sea wall in the nearby canton of Tala. Ana and Din learn that some of the engineers responsible for maintaining the wall were killed in the same manner as Blas.
Ana and Din are sent to Talagray, the capital of Tala, to continue their investigation. There, they are assisted by several imperial officers. These include Kepheus Strovi, a Legion captain with whom Din eventually begins a romance; Tuwey Uhad, an engraver who leads the Iudex division in Talagray; Uhad's assistant Tazi Miljin, a war hero; Ionia Nusis, an apothetikal; and Valiki Kalista, an engineer.
Din learns that all of the dead engineers traveled to Talagray on the same day; evidence eventually emerges indicating that they attended a meeting at the Haza family's local estate. Additionally, there is a missing associate of their group, who has not been reported dead: Kiz Jolgalgan, an apothetikal. Jolgalgan was a survivor of Oypat, the canton which was once destroyed by dappleglass. As Ana and Din track people with connections to the dead engineers, they find more bodies. These corpses include Blas's secretary and a merchant who sold supplies to the Haza family. Ana deduces that at least two killers are involved: the first poisons people with dappleglass; the second is a sublime who kills with a sharp object to the skull. Jolgalgan becomes the prime suspect for the dappleglass poisonings. Nusis tells Din that Oypat could have been saved: a cure for dappleglass had been in development, but its production was held up by red tape.
Fayazi Haza, a daughter of the family, informs Ana that her father Kaygi Haza was murdered with dappleglass at his home shortly after a party. Din investigates the estate, where he finds dappleglass in the water tank of Kaygi's bathhouse. Din realizes that the ten dead engineers were also present on the night of the party; they were part of a coterie of young officers being cultivated for patronage by the Haza family. Din and the investigators later find Jolgalgan’s body; she was killed by dappleglass after a malfunction in her lab. Finally, Nusis is killed with a blow to the skull.
Ana brings Fayazi Haza to the office of the Iudex. There, she reveals her theory of the case. Jolgalgan killed Blas. She then infiltrated the party at the Haza estate and poisoned the bathwater. While Kaygi was in the bath, he drank from a ewer of wine, which became infected with dappleglass spores. During a patronage meeting later that evening, the ten engineers drank from the same ewer, contracting the contagion from the cup and eventually leading to their deaths. Their deaths and the resulting breach in the sea wall were never intended. Jolgalgan was seeking revenge against Blas and the Hazas for the destruction of Oypat; she had learned that the Haza family used their network of patronage (including Blas) to block production of the cure for dappleglass, because the destruction of Oypat would increase the value of their own landholdings. Fayazi’s axiom is revealed to be a fraud; she is actually a twitch, a sublime with incredible speed, sent as an assassin by the senior branch of the Haza family to keep Fayazi in line and cover up their connection to Oypat. The twitch killed the secretary, the merchant, and Nusis. Ana kills the twitch by contaminating her own apartment with dappleglass and baiting the twitch into entering.
The denouement is interrupted by another leviathan attack, but the Legion successfully fights it off. Later, Ana reveals that Jolgalgan was not the sole perpetrator, but rather was an accomplice to the engraver Uhad. Uhad was present at the party at the Haza mansion, and provided a distraction which allowed Jolgalgan to poison the water tank; he later sabotaged her lab when Din was closing in on her. Uhad has been a long-term servant of the Empire; he was motivated by a desire to combat the corruption of the gentry who allowed the destruction of an entire canton for monetary reasons.
Din is promoted to become a full assistant investigator. He spends time with Strovi in Talagray before he and Ana are sent on their next investigation.
