Living alone had always felt like a sanctuary to Melanie—until strange notes started appearing around her apartment. At first, they were simple reminders she didn’t remember writing, but soon they turned judgmental, then sinister. Her belongings were misplaced, and she even found a bottle of juice she never bought in her microwave. Fearing she was losing her mind or being watched, she installed a webcam to catch the intruder—only for it to vanish the next day, replaced by another chilling message.

Suspecting her neighbor Ron, who once had a spare key, Melanie confronted him after he claimed she’d visited him the night before—something she had no memory of. As her anxiety and confusion deepened, Melanie collapsed and woke up in a hospital. The diagnosis stunned her: carbon dioxide poisoning. Her symptoms—memory loss, confusion, hallucinations—were caused by a faulty ventilation system in her apartment.

Ron had brought her to the hospital just in time, and the doctors explained that her brain had likely created the notes and strange behaviors under the influence of CO2. The danger wasn’t a stalker, but the invisible gas seeping into her lungs and warping her mind. Her obsession with true crime had only fueled the illusion, making her believe someone was targeting her.

Back home, Melanie and Ron installed a carbon dioxide detector and aired out the apartment. As her health returned, so did her clarity—and trust. What she thought was a terrifying mystery turned out to be a life-threatening hazard. But through it all, Ron stayed by her side, and with one kind note on the fridge—“Take care of yourself”—a new chapter began.