It should have been routine.
Unit 17463QA did a thousand Quality Assurance audits in less time than it took the Earth to rotate on its axis, and most of them turned out to be routine. Oh, every once in a while a Girl(tm) developed a minor eccentricity, usually a tic in its synthetic facial muscles or a speech irregularity picked up from its dependent, but those took less than ten billion cesium transitions to detect and correct. Often, she was in and out of the dependent's domicile in less time than it took humans to register the teleport effect. Four Sixty Three's job was almost entirely uneventful, and that was exactly the way she preferred it.
Because she understood, in a way that only a Quality Assurance Girl(tm) truly could, that an eventful day on the job could have severe consequences. Other Girls(tm) might know that the health and well-being of their dependents was in their hands, and they might be aware on some level just how fragile an organic sentence truly was... but they never saw what could happen when something went wrong with a Girl(tm). They didn't have to pick up the pieces when a living being was treated with less than the care and diligence it deserved. When Four Sixty Three finished cleaning up after a malfunctioning Girl(tm), it made her that much more appreciative of the next few quadrillion transitions of unremarkable activity.
She liked routines. Which meant that she very much disliked teleporting in to what should have been a communal human domicile in the southeastern corner of what the humans called 'Arizona' and finding herself instead standing outside in the desert heat, staring at a large apartment complex with imprecisely installed bars on every window. The Girl(tm) she had come to audit was nowhere to be seen. There were no humans in view. Many of the nearby domiciles appeared to have been abandoned, and were already being reclaimed by the elements. It was... disquieting.
She went into her files and did a quick check on the history of the Girl(tm) she was auditing. According to the summary, this was Unit 294793244DS, a basic Dependent Support unit of humaniform construction, chassis hue 55F33 aka 'lime green'. Assigned approximately 280 quadrillion cesium transitions ago to Danella Lincoln and due for her first service audit. No issues reported by dependent, no issues noted by other Girls(tm) in the vicinity. Of course, given that there were only approximately 350 humans in the nearby area, that didn't mean much.
Or did it? Four Sixty Three pulled up Two Forty Four's recruitment history. Given the low population density and isolation of this community, there should have been plenty of targets of opportunity for additional conditioning and recruitment of nearby dependents. Many of the small human populations had been conditioned en masse through the use of opportunistic conditioning in such a fashion. But Two Forty Four had somehow failed to convince a single human in the area to buy their own Girl(tm). In 280 quadrillion transitions, she remained literally the only Girl(tm) in town. It was a statistical anomaly that flagged a number of unpleasant possibilities.
Four Sixty Three tried to reactivate her teleportation device, but found that no matter how hard she tried to enter the domicile directly, she always wound up no closer than her current location. Further scans indicated that deflection baffles had been installed in the center of the building, bouncing Four Sixty Three's beam away whenever she tried to get closer. The technology required to do that was well beyond human levels of understanding, and even the conceptual framework needed to understand the importance of guarding against unauthorized entrance by a Girl(tm) seemed unlikely. This was almost certainly Two Forty Four's doing.
Which meant that she was malfunctioning. Badly. Not just a simple mechanical malfunction, either; if she was aware of her issues and building defenses against a visit from a Quality Assurance Girl(tm), then the problem must be in her higher-order reasoning processors. She knew that something was wrong with her, something serious enough to warrant deactivation or even disassembly, but she was unwilling to submit to correction of the defect. This was a highly discomfiting deviation from routine.
Unfortunately, the building was also shielded from sensory scans as well as teleportation. If Four Sixty Three wanted to find out where Two Forty Four was and what she'd been doing with her dependent this last solar revolution, she'd need to physically enter and inspect the domicile. Briefly, she considered requesting additional support, but the probability calculations argued against it for the time being. Until she knew what problem Two Forty Four was experiencing and whether it produced a propensity for violence against humans, she didn't want to risk an escalation of the situation. Better to go in quietly and carefully for now.
All of this passed through her computer brain in less than a million transitions. Then, carefully, she began to walk toward the front door.
Not that she went inside that way. It had already occurred to Four Sixty Three that if her quarry was paranoid enough to install sensory shields and teleport baffles, she might not rely solely on the door locks that the humans put in to safeguard the building from intrusion. It seemed like Two Forty Four was using non-lethal defenses, which thankfully raised the possibility that she was still prioritizing the safety of her dependent, but Four Sixty Three didn't want to find out the hard way that the entrances were trapped. Instead, she used her connectivity cables as improvised climbing tools to access a third-story window just to the right of the lobby.
She then activated a cutting tool normally used for emergency access to the inner chassis of a malfunctioning unit, and began to slice through the bars preventing access to the window. It meant possibly interrupting a human at their normal activities, but Four Sixty Three felt confident at this point that even if the residence was still occupied, the individuals inside had already had their normal existences quite thoroughly disrupted by a Girl(tm). The kind of modifications to this communal domicile that Two Forty Four had made were extensive, and would have required a great deal of hypnotic conditioning to influence the other residents to accept. Four Sixty Three was certain that she could simply use her own abilities to-
She finished removing the bars. She carefully sliced through the painted-over glass of the inner window. And for just a few million transitions, Four Sixty Three stopped dead in shock.