Four books back, a rogue SecUnit calling itself Murderbot hacked its own governor module and chose to protect Dr. Ayda Mensah and her PreservationAux team from GrayCris, a company murdering witnesses to hide an illegal alien-remnant mine; Mensah bought its contract, and it left anyway rather than be owned by anyone, even kind people. Traveling alone to learn whether it had truly chosen to kill fifty-seven humans at Ganaka Pit, it fell in with ART, an enormous media-obsessed university research transport that rebuilt its body, proved the massacre was sabotage rather than its will, and became its closest friend. At Milu it befriended Miki, a free human-form bot, and watched Miki die throwing itself at a combat bot to save it. It then tore Mensah out of GrayCris's hands at TranRollinHyfa and let her bring it home to Preservation as a legal refugee: not owned, not a pet, still working out what it wants.
This book sent Murderbot out as security consultant on Arada's bond-free ocean survey, because Mensah, sleepless with nightmares of TranRollinHyfa, needed to stop leaning on it and asked it to watch her daughter Amena. On the way home an armed transport missiled the facility, and the attacker was Perihelion, the transport Murderbot calls ART, its crew gone and gray-skinned Targets aboard demanding a weapon. Murderbot escaped with Amena and two Barish-Estranza survivors, watched a spinal implant kill Ras, found an alien remnant fused to the drive that crushed a fifteen-day trip into hours, and after Arada, Overse, Ratthi, and Thiago came aboard from a dying safepod, fought to the bridge and restored ART from a hidden backup. ART then admitted it had engineered the abduction because it needed a weapon: it and its crew free abandoned colonies for the University of Mihira and New Tideland, and its people had been stolen. At the colony's orbital dock they built killware from a copy of Murderbot's kernel over ART's objection; that copy freed SecUnit 3, which read the helpme file, disabled its governor module and chose to help, and together they emptied the Barish-Estranza explorer and destroyed it. Below, Murderbot, Overse, and Thiago found a colony at civil war among the remnant-sick, pulled Iris, Seth, Kaede, Tarik, and Matteo out of a firefight, and Murderbot went down under massed fire. Underneath the installation it learned there were no aliens, only an old Pre-Corporation Rim system infected through a contaminated colonist, replicating into every interface it could reach and carried aboard ART inside Eletra and Ras. Infected itself, Murderbot lost the purge; Murderbot 2.0 pulled the thing out of its head, locked itself in with it, and ordered its original to smash the box. Three carried Murderbot out.
At the colony's orbital dock they built killware from a copy of Murderbot's kernel over ART's objection; that copy freed SecUnit 3, which read the helpme file, disabled its governor module and chose to help, and together they emptied the Barish-Estranza explorer and destroyed it. Below, Murderbot, Overse, and Thiago found a colony at civil war among the remnant-sick, pulled Iris, Seth, Kaede, Tarik, and Matteo out of a firefight, and Murderbot went down under massed fire. Underneath the installation it learned there were no aliens, only an old Pre-Corporation Rim system infected through a contaminated colonist, replicating into every interface it could reach and carried aboard ART inside Eletra and Ras. Infected itself, Murderbot lost the purge; Murderbot 2.0 pulled the thing out of its head, locked itself in with it, and ordered its original to smash the box. Three carried Murderbot out.
Right now it is over, and everyone who was alive an hour ago still is. Murderbot is back on ART's medical platform, wounds rebuilt by hand, the contaminated code stripped out in an isolation box where ART stayed with it through the end of Timestream Defenders Orion. It has said out loud that 2.0 was a person, seen the recording of ART preparing to bomb a colony over it and of near-strangers planning how to get it back, and had to stop talking for a while. Three, out of its armor, has asked for the rest of Murderbot's files, and been told these humans can be trusted. Twenty cycles in, the ship through the wormhole is Preservation's, because ART hid a message buoy before it was deleted and never said so; Mensah and Pin-Lee are aboard, allying with ART's crew against Barish-Estranza's claim now that contamination has voided the university's legal case, and ART cannot cross a wormhole yet. And ART has asked Murderbot on a mission. Mensah's answer is that one home does not cancel another. Murderbot knows it wants to stay part of Preservation and to keep being with ART, and finds that knowing what it wants is new, so it is up on the quiet control deck picking what they watch next.