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 gifted young engraver, is chosen as the assistant to the eccentric Iudex investigator Anagosa "Ana" Dolabra; Din does his best to hide his severe dyslexia, a major source of shame for him. Their first assignment concerns the death of engineer Taqtasa Blas, whose body is found in a mansion belonging to the wealthy Haza family. Blas was poisoned with dappleglass, which caused plant matter to grow instantaneously through his body. Soon after their investigation starts, a leviathan breaches the sea wall protecting the nearby canton of Tala. Ana and Din learn that several of the engineers responsible for maintaining that wall have been found dead, killed in the same manner as Blas.
Ana and Din travel 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 develops a romantic bond; Tuwey Uhad, an engraver who serves as the head of the local Iudex division; Uhad's assistant Tazi Miljin, a decorated war hero; Ionia Nusis, an apothetikal; and Valiki Kalista, an engineer.
Din discovers that all of the deceased engineers had gathered at the Haza family's Talagray estate upon the same day. The investigators also identify a missing associate from their group: Kiz Jolgalgan, an apothetikal and a survivor of Oypat, the canton destroyed by dappleglass. Jolgalgan becomes the chief suspect for the poisonings. Nusis tells Din that Oypat's destruction could have been prevented, as a cure for dappleglass was in development but its production was stalled by red tape. Meanwhile, more bodies are discovered: Blas's secretary and a merchant who sold goods to the Hazas. These two were killed by a sharp blow to the skull, pointing toward a second killer: a type of sublime known as a twitch, with enhanced speed.
The case takes a sharp turn when Fayazi Haza reports that her own father, Kaygi Haza, was also killed by dappleglass at his home after a party. Din's inspection of the estate determines that the poison was introduced to the water tank supplying Kaygi's bathhouse. He ascertains that the ten engineers were also present that night, part of a coterie of officers being cultivated for patronage by the Haza family. Soon after, Jolgalgan is found dead from what appears to be a laboratory accident, and 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. One of Fayazi's aides is revealed to be an assassin sent by the senior branch of the Haza family to keep Fayazi in line and cover up their connection to Oypat; she is the twitch who killed the secretary, the merchant, and Nusis. Having contaminated her own apartment with dappleglass, Ana kills the twitch by baiting her into entering.
The denouement is interrupted by another leviathan attack, which the Legion successfully repels. Later, Ana reveals that Jolgalgan did not act alone; she was assisted by the engraver Uhad. He created a diversion during the Haza party, allowing Jolgalgan to access the water tank unnoticed, but later sabotaged her laboratory when the investigation drew too near. Uhad, a steadfast servant of the Empire, 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 some time with Strovi in Talagray before he and Ana are sent on their next investigation.
