Marcus Williams knew the Johnson Space Center the way a priest knows a confession booth — not the inside details, necessarily, but the shape of it, the angles where things hide.

He had been cleaning offices here for twelve years. Twelve years of emptying trash cans and vacuuming carpets and wiping coffee rings off desks that people would sit at again on Monday morning. Twelve years of seeing what people did when they thought nobody was looking.

Which was most of the time.

The scientists at JSC were no different from anyone else. They smiled at you in the hallway and called you Marcus, which was close enough to Mark, and asked if you had seen their pen, and you handed them the pen because the pen was always on the desk they were looking at, and they said thank you without looking at you, which was the way things worked.

But in the break rooms, in the stairwells, in the moments between the meetings — that was where you learned things.

Like the fact that Dr. Susan Park, who worked in the astrophysics division, had been coming in at 2 AM for months. Not the dramatic kind of late night where she was crying or yelling at a computer screen. The quiet kind. She would sit at her desk, staring at a monitor that displayed nothing you could see with your eyes — gravitational wave data, she had once explained, when a curious intern had asked. The waves from colliding black holes. Tiny ripples in the fabric of everything.

Like the fact that her data had been flagged by the review board six months ago and marked as "possibly instrumental error."

Like the fact that she had requested access to the old sensor archive — the data from three sensor arrays that had been decommissioned in 1987 — and the request had been denied.

Marcus knew these things because he had been in the break room when Dr. Park talked to her friend in the library division. He had been mopping the floor nearby, which meant he was essentially part of the furniture. People talked around Marcus the way they talked around a plant.

"Three arrays," the friend had said. "That's impossible."

"Not if they were calibrated differently," Dr. Park had replied. Her voice had been flat. Not sad. Not angry. Just flat, the way a river is flat before it goes over the edge.

Marcus had kept mopping. He had reached the corner of the break room where the mop bucket caught the fluorescent light in a way that made rainbows on the linoleum, and he had paused there, listening.

"What kind of signal?" the friend had asked.

Dr. Park was silent for a moment. When she spoke again, her voice was so quiet Marcus had to press his ear toward the door.

"A signal that was sent a very long time ago," she said. "And that we should have answered."

The intern who had been sitting at the table — a young woman with blonde hair and a notebook that she used to write things she probably would not read — asked: "Did someone answer?"

"No," Dr. Park said. "That's the thing. Nobody answered. And that is going to be the most important thing anyone ever fails to do."

Marcus finished mopping that corner. He folded the mop and hung it up. He pushed the bucket into the closet and closed the door. He went back to his cart and moved to the next office.

In that office, he found a notebook on the floor behind the desk. It had fallen when someone had knelt to retrieve something — a pen, probably, or a paperclip. He opened it. The writing was in Dr. Park's hand. Diagrams. Numbers. Three intersecting curves that looked like a fingerprint or a heartbeat or —

He didn't understand the diagrams. But he understood the hand that had written them. It was the hand of someone who had stayed late, who had not gone home to her husband or her dog or her television, who had sat in this room and drawn these curves on this paper because something in them had required her attention.

Marcus put the notebook back on the floor. He did not take it. He did not report it. He vacuumed around it, carefully, so the dust would not get in the vents, and moved to the next office.

But he kept thinking about those curves. Three intersecting lines. He had seen things like that before — not in a science lab, but in the old auto plant, when he used to align engine parts. Three cylinders firing in sequence. If one was off, the whole engine shook. If all three fired at once —

He shook his head. He was a cleaner. He cleaned offices. He did not think about astrophysics.

But he went back to the break room the next day and stood by the coffee machine and waited until Dr. Park came in.

"Doctor," he said.

She looked at him. It was a polite look. The kind of look you give to the person who empties your trash.

"Marcus," she said. "How are you?"

"I had a question."

She hesitated. Then she came over. Not all the way — she stayed two steps away, which was the polite distance. "What is it?"

"The curves in your notebook. The three lines. They don't look like waves."

Dr. Park went very still. "What do they look like?"

"Like a fingerprint," Marcus said. "Like someone left their hand on something and it's still there."

She was quiet for a long time. The coffee machine gurgled behind them. Somewhere down the hall, a computer beeped.

"You know," she said finally, "most people don't look at the curves. They look at the data. They look at the numbers. But the curves —" She stopped. "Nobody looks at the curves."

"I look at the curves," Marcus said.

She nodded. Not thank you. Not exactly. Something that had thank you in it but was bigger than thank you, the way a river is bigger than the water that flows through it.

"I'll show you," she said.

And she did. Over the next three weeks, Marcus Williams learned about gravitational waves and sensor calibration and the fact that something had been detected by three independent arrays on the same day in 1987 and buried because it didn't fit any known model.

He didn't understand all of it. But he understood this: the world was bigger than the people who worked here wanted it to be, and they were afraid of the bigness, and they were hiding from it in the same way people had always hidden from things they could not control.

On the last day he showed him the curves, Dr. Park said: "I'm going to try to publish this. They'll say it's error. They'll say it's noise. They'll say a lot of things."

"What will you do?" Marcus asked.

"I'll keep looking at the curves," she said. "That's all any of us can do."

Marcus went home that evening and sat in his apartment in Houston and looked at the sky. It was cloudy. He could not see any stars. But he knew they were there, behind the clouds, firing their sequences into the dark, waiting for someone to look at the curves.