Meshner and the rest of the crew are supplementing Kern’s processing power during the battle when Bianca is killed. While attempting to plot an escape route with Fabian, Meshner has a seizure. His experimental neural implant activates, causing him to experience one of Fabian’s Portiid memories—an “Understanding”—as a vivid hallucination. He realizes he is in a virtual space created by his own mind to process the alien data.

Meshner follows a connection to Kern, who appears as a giant, severe avatar in a virtual representation of the battle. She scolds him for draining her processing power with his “existential crisis” and explains that his implant has created an uncontrolled simulation of his own cognitive functions. She isolates his consciousness to prevent him from crippling the ship. Before she can purge him from the system, Meshner uses the virtual map to show her a new strategy: The large enemy ships have split into two factions that are fighting each other, creating safe corridors the Lightfoot can use to escape. As Kern considers the plan, Meshner regains consciousness in the physical world, where his crewmates are treating him.

Having escaped the battle, the Lightfoot crew learns that the three alien ships that protected them are now following them and have sent coordinates for a rendezvous. The crew debates the risk. Portia argues that they must investigate to honor Bianca’s sacrifice and understand the threat. They proceed toward the coordinates, which will take them two months to reach.

During the journey, Helena analyzes the aliens’ transmissions. She discovers a pattern: The ratio of visual data to numerical data correlates with the message’s emotional intensity. She concludes she is dealing with a species for whom visual display is a primary form of communication and focuses her efforts on translating this visual language. As they near the destination planet, they detect a chaotic flood of similar signals, suggesting a technologically advanced and potentially hostile civilization.

After two months, the Lightfoot arrives at the rendezvous point. Scans of the destination planet reveal it is a water world with extensive orbital structures. Kern’s analysis of the alien ships’ mass and momentum supports a new theory: The vessels are filled with water. At the meeting point, one of the alien ships creates a large, transparent globe of water held together by a magnetic field, with another ship attached by an umbilical. When the crew receives a clear docking invitation in a recognizable Old Empire format, Portia volunteers for the first-contact mission. Helena, having developed a rudimentary grasp of the aliens’ visual language, agrees to go with her.

As the Lightfoot approaches the water-filled sphere, Helena briefs Kern on her translation progress. She can now produce visual signals to convey basic concepts like “we come in peace” (195). Meanwhile, the crew notes that Meshner has been granted unusually high-level access to Kern’s systems. Portia and Helena don their suits, which are rated for both vacuum and water. Kern admits that she secretly built an electromagnetic pulse weapon for the ship, but cannot use it here, as it would destroy the magnetic field containing the water, leaving the ambassadors without support if the meeting turns hostile.

The Octopus Paul emerges from his ship into the water globe to meet the visitors. The sight of Helena’s humanoid form triggers a deep, ancestral fear recorded in his species’ collective memory, but his curiosity overcomes it. Helena displays a screen with colors and shapes, and Paul, aided by his ship’s systems and his own distributed nervous system, understands it as a message of peace. He responds with a complex display of color and movement on his own skin.

Mistaking the newcomers’ simple signals for a lack of sophistication, Paul approaches and touches Helena’s suit. The gesture causes Portia to make a threat display, and Paul realizes that these aliens do not communicate through touch. As his tentacles explore Helena’s suit, his ship’s sensors transmit a sudden, overwhelming warning to the entire octopus crew: The aliens are a source of immediate danger. Paul instantly recoils, releasing an ink cloud as his people’s emergency protocols activate.

While monitoring the first contact, Kern detects an unfamiliar signal coming from the next planet in the system. The broadcast is in Imperial C, the language of Old Empire humans, and appears to be a fragment of a natural history text. Kern is shocked to find potential survivors of her long-dead civilization, but as an AI, she feels a frustrating void where the corresponding emotion should be. To experience what she believes is the correct human response, she secretly accesses Meshner’s neural implant, using his brain’s architecture to generate feelings of awe, hope, and dread. The intrusion causes Meshner to have another seizure. Distracted by the experience, Kern allows a subroutine to automatically reply to the Imperial C signal. The moment her acknowledgment is sent, the situation with the octopuses turns hostile.

The narrative flashes back to the past.

Aboard the Aegean, Senkovi works obsessively with the octopuses he is uplifting. He decides to provide them with a complete virtual simulation of Damascus, their new world, allowing them to see how they can shape it. While the octopuses explore the simulation from their tanks, Senkovi works for days without rest. Only when he is finished does he notice a series of urgent messages from Baltiel regarding an emergency with Lortisse on Nod.

On Nod, Lante informs Baltiel that Lortisse has been stabbed by a native tortoise-like creature and went into severe anaphylactic shock. Lante stabilized him and has identified the injected substance as the complex organic fluid she previously discovered in other Nodan creatures. Lante theorizes it is an infectious organism, like a slime mold, that cannot directly harm human cells but triggers a catastrophic and repeating immune response. She warns Baltiel that this attack proves the planet is more dangerous than they assumed. When Baltiel deflects responsibility, Lante rebukes him for his poor leadership.

In an interlude, the Nodan organism describes itself as a collective “we” and details a journey through a hostile environment (which readers understand to be the body of Lortisse) where it divides, explores, and learns. Survivors pass on knowledge to the whole. This journey culminates in the discovery of a “source of the lightning” (231)—Lortisse’s nervous system—which becomes its new home.

Days later, Lante reports to Baltiel that Lortisse is awake and recovering. She believes his immune system has destroyed the alien organism, as his blood is now clean. In the weeks that follow, however, Baltiel sinks into a deep depression, feeling a lack of purpose now that their exploration has stalled and they remain cut off from Earth. 12 days after Lortisse’s apparent recovery, a terrified Lante summons Baltiel with urgent news: New scans show the organism survived and has migrated to Lortisse’s brain.

After taking medication to restore his focus, Baltiel reviews the scans with Lante. They reveal the Nodan organism has replaced Lortisse’s corpus callosum, the nerve tissue connecting the brain’s two hemispheres. Amazingly, Lortisse shows no signs of cognitive impairment; the organism is somehow facilitating communication between the hemispheres. Unsure of the long-term effects but fearing the organism could become destructive, they agree to inform Lortisse and prepare a risky procedure to remove it.

The Nodan organism’s narration continues. Now established between the two hemispheres of its host’s brain, it listens to the flow of information. From this, it learns of a vast world beyond its vessel: space, other planets, and complex new concepts. In order to process this new reality, the organism is forced to grow and evolve. After generations of passive learning, it begins to actively alter the information passing through it, effectively speaking to its host in the host’s own neural language.

When Lante explains the situation, Lortisse is unnervingly calm. As she prepares a treatment, he refuses it, claiming in the first person plural that it would “upset the balance These-of-We have achieved” (244). With an uncontrollable smile, he describes a new, vast awareness. When Lante tries to administer an injection, Lortisse fights back with unnatural strength. He extracts a fluid sample from his own body with a syringe, then bites Lante’s hand as Baltiel and their crewmate Rani intervene. He breaks his own bones to escape their hold and fatally wounds Rani, forcing his infected blood into her. As the parasite withdraws from his dying mind, Lante kills him with a cutting tool.

Baltiel seals the lab and tries to save Rani, sending a wounded Lante to retrieve the treatment. Alone in the lab, Lante panics, fearing she was infected by Lortisse’s bite. Before she can act, Lortisse’s corpse reanimates and injects her with the parasitic fluid. Soon after, Rani revives, her personality subsumed by the parasite. Speaking as “We-in-Rani,” she tells Baltiel, “We're going on an adventure” (255), and that she will now live forever in their collective memory. Lante appears, also infected, and repeats the same phrase, which has become the organism’s unnerving refrain. Realizing he is the last human left, Baltiel grabs an emergency axe to defend himself.

Senkovi receives a frantic call from Baltiel, who is flying a shuttle from Nod. Baltiel confesses that he killed Lortisse, Lante, and Rani with the axe after the parasite took them over. Senkovi then realizes with horror that Baltiel is flying directly toward the Aegean. When confronted, Baltiel’s personality shifts, and the parasite speaks through him, announcing, “[W]e’re going on an adventure” (269). The Nodan organism uses Baltiel’s command codes to lock Senkovi out of the ship’s defenses, expressing its desire to explore the “vastness” it learned of from its human hosts. Unable to regain control in time, Senkovi sends a final warning to the octopus civilization on the planet Damascus. In response, the octopuses coordinate the planet’s orbital mirrors, focusing them into a single, powerful beam of light that incinerates Baltiel’s approaching shuttle.