This novella is set on Preservation Station, a space station independent of the Corporation Rim, a region of space dominated by corporate interests. The first-person narrator is Murderbot, a self-aware construct made of cloned human tissue and mechanical augments, including built-in energy weapons. A rogue SecUnit, a type of human-machine construct designed for security, Murderbot now works as a security consultant for Dr. Mensah, a planetary council leader on Preservation.
When a dead human is discovered in a corridor junction of the station mall, Murderbot examines the body alongside Mensah and Senior Security Officer Indah. The body has no identification marker and a broken feed interface, a device for digital communication. Mensah privately asks whether the murder could be connected to GrayCris, a hostile corporation threatening Preservation. Murderbot lacks data to assess but agrees to work with Station Security at Mensah's urging.
The narrative recounts their strained relationship. When Mensah disclosed Murderbot's nature to the council, Indah tried to have it removed, calling it a dangerous weapon. Mensah insisted Murderbot is a person. Two restrictions were negotiated: Murderbot would not hack non-public systems or conceal its identity. Shortly afterward, someone leaked a photo identifying Murderbot to the newsstream. Mensah responded by giving Murderbot intel drones, which it uses to maintain a surveillance network around her.
At the crime scene, Murderbot determines the perpetrator used a cleaning field after the attack, since the victim's clothes lack contact DNA. The head wound and insufficient blood confirm the victim was killed elsewhere. The brightly colored clothing is recycler-produced fabric from the Corporation Rim, suggesting someone posing as a conspicuous visitor to move unnoticed. Indah dismisses Murderbot from the scene.
Murderbot investigates independently, communicating with Tellus, a bot at the transient housing block. Together they locate a room registered to Lutran, where a matching scarf confirms the identification. Searching docked transports for Lutran's arrival ship, Murderbot encounters an automated cargo hauler responding with garbled error codes. Murderbot calls Ratthi, a survey academic and friend, and Gurathin, a more adversarial but dependable colleague, as witnesses. Inside the transport, they find dried bloodstains and a travel bag, confirming the original murder scene.
Indah introduces Special Investigator Aylen, who asks directly whether Murderbot killed Lutran. Murderbot provides drone footage proving it was elsewhere. Aylen shares surveillance video showing Lutran entering the transport but no one else entering or exiting. A second clip shows a delivery cart arriving and departing seven minutes later, apparently used to move the body. The killer avoided all cameras, and no one can determine how.
Indah assigns Murderbot to accompany Aylen to the Merchant Docks to interview the crew of the Lalow, an outsystem cargo ship. When Aylen and Port Authority Supervisor Gamila board the ship, the crew takes them hostage at gunpoint, believing them to be corporate raiders. Murderbot breaks its promise not to hack non-public systems, accessing the Port Authority's SafetyMonitor to relay Aylen's distress signal. Balin, a Port Authority bot that had seemed inert, extends to twice Murderbot's height and forces the hatch open. Murderbot storms the ship, neutralizes the crew, and rescues the hostages.
During interrogation, the crew claims to be simple traders, but biometric scanners reveal involuntary recognition when Aylen says the name "Lutran." One crew member, Miro, reveals the truth: BreharWallHan, a mining corporation, runs a forced labor operation in an asteroid belt, where contract laborers have been trapped so long their children are born into captivity. An escape pipeline smuggles laborers to safety, and Lutran arranged their next steps. The Lalow was transporting ten refugees, including three adolescents.
Murderbot reviews dock surveillance and discovers the refugees entered the Merchant Docks but never appear on any exit camera. To investigate, Murderbot persuades Indah to grant temporary system access for a diagnostic, demonstrating vulnerability by hijacking the office displays without triggering alerts. The diagnostic finds no trace of hacking, and the investigation stalls.
A breakthrough comes when a tech reports that a transfer module, a detachable cargo container used to move goods between ships, is missing from inventory. Lutran loaded the refugees into the module for transfer to his transport, but someone redirected it to a BreharWallHan ship hiding near the station's preserved colony ship. Murderbot argues the search must stop: If agents monitoring the compromised Port Authority systems learn the module has been found, they will kill the refugees. Murderbot admits it was wrong about the systems being clean.
From Mensah's secure council office, Indah directs the station's responder ship to locate the module. The responder finds it clamped to the hostile vessel's hull. Murderbot volunteers for the rescue, using a life-tender, a primitive emergency vehicle from the colony ship's original safety equipment, to reach the vessel undetected. Inside the module, the refugees huddle cold and frightened. Murderbot loads six into the life-tender for the first trip back.
Before a second trip, the hostiles try to dump the module into space. Murderbot signals the responder and fights into the ship, disabling an armored hostile and securing the remaining refugees. The responder's intervention team boards and takes control. One refugee, realizing Murderbot is a SecUnit, shoots it in the back out of fear. Murderbot declines to file a complaint.
Murderbot proposes two approaches to identify the local actor: a surveillance audit cross-referencing station data, and a bait operation using a refugee as a lure. While crossing the Public Docks in response to a spoofed feed message, Murderbot's drones detect a crane falling from above. Murderbot dodges and pieces together the answer: The only entity present at every critical moment, with full system access and the ability to traverse the station's exterior hull, is Balin. Balin walked outside the station to enter Lutran's transport through the module lock, killed Lutran with the rods in its hatch-decoder hand, sterilized the body, called a delivery cart to move it to the mall, and returned without appearing on interior cameras.
Murderbot confronts Balin in Gamila's office. Balin launches a code-based cyberattack and a high-speed limb strike; Murderbot deflects both and fires explosive projectiles into Balin's carapace, revealing military-grade armor beneath the general-purpose exterior. Balin is a CombatBot, a bot with concealed combat capabilities. Records show it arrived on Preservation 43.7 years ago posing as a refugee bot. Its deploying corporation was later absorbed in a takeover, and its dormant combat function remained inactive until BreharWallHan obtained its command codes and activated it to destroy the refugee pipeline.
Balin smashes through the office window into the docks. Murderbot clings to it, firing into its undercarriage as they fall. On impact, JollyBaby, a cargo bot, interposes its massive hand between them. Dozens of station bots have gathered, recognizing Balin's exposed CombatBot designation on the feed. Their silent presence sends an unmistakable message: They know what Balin is and will protect humans and each other. Its stealth permanently compromised, Balin shuts itself down.
Afterward, Indah tells Murderbot she was not the one who leaked its photo and considers them on the same side. Murderbot, caught off guard, deflects. Indah authorizes Murderbot's payment and asks whether it would take another contract the next time something weird happens. Noting that the expected wave of depression at the prospect has somehow not arrived, Murderbot replies, "Only if it's really weird."