Brain implants had become very popular for a wide variety of purposes and reasons.
Some needed constant access to the flow of data from all over the world to make informed and impactful decisions. Others just wanted to post on social media directly from their brains. Others still needed to interface with technology in a way that only having technology directly in their brains could allow. The procedure was safe and mostly painless, if a bit pricey still.
Mark's reasoning behind getting a brain implant was that he needed to be able to monitor marketing data for his boss while handling the numerous other tasks shoved on him by said boss. Because that function was so necessary for his job, the implant couldn't be remotely disabled to keep him "on task," so sometimes he would take a peek at less relevant things on the job. He had never been good at separating business and pleasure.
A certain article caught his mind's eye as he browsed through the implant, making him take the focus off the computer in front of him. A popular internet celebrity, StreamAbby, was being discussed on some anonymous board somewhere. The comments indicated that she had been acting unusual recently, promoting products that no one knew she had a contract for and suddenly doing complete reversals of her cheery persona. Apparently, she had made threatening comments towards a government official at one point, even as she had sworn never to make her streams about politics.
Everyone knew StreamAbby had a brain implant. She wouldn't be able to stream her life 24/7 for the entire world if she didn't. However, because of how many eyes were on these behaviors, whispers were going around that she was being remotely controlled. Sure, more "grounded" people chalked it up to a stress-induced breakdown from having eyes on her constantly, but she was not the first case of behavior changes that occurred after receiving a brain implant.
Mark shuddered. His memories of a certain incident were blurred, but whoever had left them had not done the most thorough job of erasing them. They were still there. He remembered a knife, blood on his hands, a great fire to dispose of a body. He didn't know how to do these things on his own, but somehow, something or someone had put that knowledge there and commanded him to use it.
A voice, or something that registered as a voice, came to him inside his head. "Meet Abigail Westerman at the corner of 4th and 7th."
That was outside his office. Who was Abigail Westerman? The voice informed him that this was StreamAbby's true name. Mark gasped, his heart pounding in his chest.
It was happening again. Something was attempting to hijack him. "No," he mumbled to himself, clinging to his desk in an attempt to suppress the urge to walk away from his desk. "Stop!"
The brain implant's signals took priority. The panic in his chest stopped, and Mark slowly got up to meet Abigail Westerman on the street corner outside his office. His boss called out to him, but the sound was so distant that it might as well have been a call from across the world. Mark watched his body get up and move, and for a moment he understood what it meant to be "locked in." He felt as though he was standing on a tiny island in his mind, surrounded by a sea of information and instructions that weren't supposed to be there. Alternately, it was like being shoved into an overhead compartment inside his own mind. There was a distinct feeling of being imprisoned as something else took hold.
Some portion of what was still him mentally yelled out. He could hear his voice in his mind's ear well enough, but it distorted once the implant signal latched onto it and replaced it. A fragment of helplessness and hopelessness passed through the corner of his mind that was still his own. He could only watch as he walked out of his office, made his way to the city street, and met with Abigail. The conversation that ensued was a blur, as though it was being deliberately censored to avoid Mark knowing what was going on. It was like the murder all over again.
The blurry words stopped, and Abigail walked away, but not before she gave Mark a brown paper-wrapped package. Inside his mind, Mark hoped that he would be given control again, or that at least the hijacker would walk him back to his desk. Alas, the miracle never happened. Mark proceeded to walk across the street with the package, going further and further away from his office. He had never been in the part of town he was heading to.
All Mark could do was sit and watch as his control of himself slipped away entirely.