Plague ravages Great Nest, halting contact between peer houses. Portia organizes a citywide scientific effort, asserting that the few immune spiderlings inherited resistance from infected-resistant progenitors. Despite objections about the nature of Understandings, the emergency compels cooperation. Bianca privately admits early symptoms; Viola, a leading researcher, also declines. Fabian supports with supplies and coordination.

Drawing on Viola’s lifelong studies and ant-colony analytical engines, Portia reviews the “language of the body,” a coded record correlated with parentage. Ants comparing samples from three immune spiderlings reveal a new shared passage that might encode plague resistance. Yet Viola warns they can read but cannot write to this inner book, leaving the discovery seemingly unusable as despair spreads.

Bianca, worsening, visits the dying Viola and returns with a crucial revelation: a deeper, compact second code—the Messenger within—always present when new Understandings are laid down from the egg onward. Viola’s work isolates this artificial layer, which Portia recognizes as the nanovirus guiding their species’ inheritance and advancement.

Portia secures Viola’s specialized ant colonies and, with other scientists, isolates both the immune fragment and the nanovirus Messenger. As the city collapses and many enter late-stage madness, Portia has a serum prepared that pairs Message and Messenger. Refusing to risk Fabian, she leads a team to restrain the feral Bianca and injects the serum near the brain, wagering one life to test a cure that could save Great Nest.