Marcus noticed the pattern because he worked from home and paid attention to details other people ignored. The woman in 4B left her apartment at 7:15 AM every weekday morning. She returned at 6:42 PM. Always alone. Always carrying the same black leather bag.

He knew these times because he watched from his window across the narrow alley that separated their buildings. Four stories up, facing east, perfect sight line into her living room if she didn’t close the blinds. She never closed the blinds.

For three months Marcus documented her routine in a notebook he kept in his desk drawer. Monday through Friday, precise as clockwork. Weekends varied slightly but she always left before noon and returned before dinner.

The notebook grew thick with observations. What she wore. What she ate. Which lights she turned on when she came home. The way she always checked her phone immediately upon entering, standing in the exact center of her living room like she was waiting for a signal.

Marcus told himself this was normal curiosity. They lived alone in a city full of strangers. Knowing your neighbors was practical. Safety awareness. Nothing creepy about paying attention.

Then one Tuesday she didn’t come home at 6:42 PM. Marcus watched the clock tick past her usual time. Seven o’clock. Seven thirty. Eight. Her lights remained dark.

He felt something tighten in his chest that he recognized as disappointment but told himself was concern. Good neighbors worry about each other. That’s all this was.

At 9:17 PM her lights flickered on. Marcus rushed to his window and saw her pacing in the living room. She looked different somehow. Her movements were jerky, unnatural, like a puppet being operated by someone learning the controls.

She stopped pacing and looked directly at his window. Across forty feet of alley space, their eyes met. She raised one hand and pointed at him. Not waving. Pointing. Accusing.

Marcus stepped back from the window, heart hammering. She couldn’t have seen him through the distance and darkness. He was careful. Always careful.

His phone buzzed on the desk. Unknown number. Text message with no words, just an attachment. He opened it before thinking better of it.

The photo showed him sitting at his desk. Taken from outside his window. Today. Within the last hour.

Another message appeared. “You watched for three months. I watched for four. We should talk about boundaries.”

Marcus spun around to face his window. The woman in 4B stood in his alley, looking up at his floor, phone raised. She waved when she saw him. Same accusing gesture.

He backed away from the window and grabbed his notebook, shoving it into his desk drawer. This was nothing. Coincidence. She couldn’t prove anything. He had never left his apartment. Never approached her. Never spoken.

His phone buzzed again. “Page 47 of your notebook is interesting. The page where you wrote about what you would do if I ever changed my schedule.”

Marcus felt his stomach drop. He had written that. Buried in the middle of three months of observations. Details about her locks. Her habits. The best time to approach if he ever decided to introduce himself properly.

“How do you know about page 47?” he typed back before he could stop himself.

The reply came immediately. “Because I’ve been reading over your shoulder every night when you write. You sleepwalk sometimes. Leave your door unlocked. Walk the hallway with your notebook.”

Marcus looked at his apartment door. The deadbolt was engaged. He always locked it. Always.

Except he didn’t remember locking it tonight. Didn’t remember much about the last few hours actually. The boundary between watching and being watched had gotten blurry somewhere around month two.

His phone buzzed one final time. “Tomorrow I leave at 7:15 AM. You should come with me. We have so much to discuss about obsession. Bring page 47.”

Marcus spent the night sitting by his door with a kitchen knife, waiting for footsteps that never came. At 7:14 AM he looked through the peephole and saw her standing in the hallway, facing his door, holding a notebook that looked exactly like his.

She knocked three times and waited. Marcus held his breath and made no sound. Some conversations were better left unfinished.