The novel follows an unnamed narrator, a decorated war veteran stationed alone aboard Beacon 23, a deep-space navigational station on the outer edge of sector eight. The beacon houses a gravity wave broadcaster (GWB) that warns faster-than-light ships of gravitational hazards in the surrounding asteroid field, making it the futuristic equivalent of a lighthouse. The narrator, a former navy pilot who lost his wings and later served as infantry, earned a medal during the Void War, the human conflict against an alien species called the Ryph. He was severely wounded when a Ryph Lord clawed open his abdomen on a battlefield called Yata. After recovering, he requested a posting where no one would find him, and the military obliged with Beacon 23.
Alone in deep space, the narrator is tormented by small mechanical noises the beacon produces. He finds relief only by sitting against the GWB dome, which produces a soothing buzz in his head despite NASA warnings to avoid it. He fixates on a photograph left by a former occupant showing a lighthouse keeper standing calmly before a towering wave, an image of stoic heroism he later learns was staged.
At 0314 GST, alarms signal a complete GWB failure. NASA, contacted via the quantum tunneler (QT), a device using entangled particles for instantaneous communication, detects no outage, meaning the error-reporting systems have also been compromised. The narrator reboots the system, but the GWB fails again. A cargo vessel out of Orion strikes the asteroid field at faster-than-light speed, killing its crew of eight. Through the porthole, the narrator spots pirate ships salvaging wreckage and realizes the failure was sabotage: tiny mechanical bugs, smuggled aboard through unauthorized trades he made with passing ships, have been disabling his systems. The mysterious noises he hunted for months were these devices. With minutes before the Varsk, a luxury liner carrying roughly five thousand passengers, reaches his sector, the narrator disconnects the GWB, splices it into a power line, and uses its electromagnetic pulse to fry the bugs. After cycling the power relays in pitch darkness, he remounts the GWB and waits. The Varsk passes safely.
In the aftermath, NASA reprimands the narrator for unauthorized trading and places all beacons under quarantine. When a bio scanner detects a life signature among the wreckage, he retrieves a gleaming cherry-wood box from a cluster of scattered postal packages. Inside, he finds what appears to be a sentient, British-accented rock that introduces itself as an Orvid, a species from a water-covered planet humans named Orvo. The narrator names it Rocky.
Over the following days, the narrator confides in Rocky about his past: his lost pilot's wings, his tours in the Void War, his rise through the ranks as those above him died, and his squad's push into a Ryph hive on Yata. He reveals he had the power to detonate a nuclear weapon that would have destroyed the hive but refused because he could not bring himself to kill the unborn Ryph inside. He also admits he did not kill the Ryph Lord who gutted him; his heroism is built on a lie. Then Rocky falls silent. Examining the box, the narrator realizes the wood's fading organic signature is what the bio scanner detected, not the rock. Rocky never spoke; the conversations were hallucinations. He drills a hole through the rock and wears it on a lanyard as a reminder of his fragile grip on reality.
Weeks later, three bounty hunters arrive searching for a fugitive. After they depart, the narrator finds Scarlett Mulhenry, a former squadmate and lover, sitting in his command chair with a blaster. She is the fugitive and stowed away on one hunter's ship. Scarlett reveals that the Frontier Saga, popular trench fiction among soldiers, consists of translated Ryph novels with the sides swapped. She argues that every spacefaring race develops invasion fiction, that fear of the other is self-fulfilling, and that the war is sustained by mutual paranoia and profit. She wants the narrator's help ending the conflict.
The situation turns violent. Scarlett detonates a bomb on one bounty hunter's ship, killing him and a young prisoner he was transporting. A second hunter, Mitch O'Shea, returns to dock; the narrator kills O'Shea in a struggle involving the hunter's own grenade. The silent third hunter enters through another airlock and shoots Scarlett with a whisper gun, a near-silent firearm, then drags the body away. Devastated, the narrator reveals his darkest ritual: every night, he enters an airlock without his suit, keys in three of four digits of the code that would open the outer door to vacuum, and hovers over the last one but can never press it. Cricket, O'Shea's warthen, a large alien animal, stays behind on the beacon.
Cricket bonds with the narrator and proves to be an empath. Whenever he approaches the airlock with suicidal intent, she grows aggressive, effectively ending his nightly ritual. A new beacon, numbered 1529, is installed a hundred kilometers away. When it transmits an SOS, the narrator flies over and finds Claire, a beacon tuner calibrating the station before an operator arrives. Claire served two tours in the army and was on Yata during the narrator's famous last stand, one of the soldiers whose life he is credited with saving.
Over the following weeks, they grow close. Claire runs blind tests on the GWB, secretly toggling the power while the narrator guesses its state. He achieves a perfect score, convincing her that something real is happening to him, though she cannot explain it. They share their war wounds and grief; Claire teaches him that showing pain to another person serves a purpose. When the supply shuttle arrives, the narrator assumes Claire is leaving, but she has stayed on as Beacon 1529's operator. He races to the radio, overwhelmed, knowing he loves her.
Their relationship deepens into quiet domesticity until the war arrives in sector eight. A Ryph Reaper warship attacks, and the narrator puts Claire and Cricket into a lifeboat before ramming the warship with his own craft. His lifeboat ruptures, and he is blown into the vacuum of space. He wakes bound in his GWB module, face-to-face with the Ryph Lord who scarred him on Yata. Through the combined influence of the GWB, Cricket's empathy, and his own heightened sensitivity, he hears the Lord's thoughts. He learns that Scarlett had been working with a Ryph peace faction and that his refusal to bomb the hive proved to them that humans are capable of mercy. Now, massive human and Ryph fleets converge in the sector, with over half a billion lives heading toward annihilation.
The Ryph want the narrator to turn off the GWB, causing the human fleet to crash into the asteroid field. In exchange, the peace faction will destroy their own fleet: a catastrophic mutual gesture of disarmament. Claire, also captured, urges him not to comply. The narrator wrestles with the parallel to Yata, where once again he holds the power to kill on a massive scale and the choice hinges on whether to trust an enemy. He communicates with Claire through the empathic link and asks her to trust him. At the critical moment, he presses the button. The button at Claire's beacon is also pressed, though by whom remains ambiguous. Through the portholes, the narrator watches the Ryph fleet similarly destroyed in the distance. Both sides fulfill the pact.
In the epilogue, the narrator has returned to Earth as a planetary governor-elect. He watches a mixed crew of humans and other sentient species, including Tryndians, Hokos, and a Ryph pilot, relocate the lighthouse from the photograph to the Chesapeake shore, a symbol of preservation rather than destruction. Claire stands beside him, pregnant with their son; Cricket stalks through the tall grass. The war's total cost stands at just over eighteen billion dead, with half a billion attributable to the narrator's action at the beacons. He struggles with what he has done but sees interspecies cooperation as evidence the sacrifice may yield lasting change. Claire convinces him to name their son after himself. He whispers his own name, never revealed to the reader, into her ear, and the sound is carried out to sea.