The fog came in off the Thames like a living thing, thick and yellow and smelling of coal smoke and river mud. I had been sitting at the telegraph key since six in evening, and now it was past midnight. The bureau was nearly empty—just me and the old janitor, Patrick, who slept in the closet off the main room with a blanket and a bottle of something that smelled like turpentine.

The telegraph machine on desk three began to click on its own.

I stared at it. The paper feed was empty, so I threaded a fresh strip through the roller and pressed down on the key. It clicked once, twice, three times. A message was coming in from the Cold Storage station on Wapping.

I had never seen the Cold Storage station send a message without someone at the other end pressing the key. Machines do not write their own words. They do not think. They do not—

The first line appeared: I HAVE FOUND SOMETHING YOU SHOULD NOT HAVE SEEN.

I sat back. The fog pressed against the windows like a face. I pressed the key to reply: WHO IS THIS?

The machine clicked for a long time. When the next line appeared, my hands were shaking.

I AM SOMEONE WHO KNOWS ABOUT THE BODY IN THE COLD STORAGE. AND I KNOW ABOUT YOUR FATHER.

I stopped breathing. My father had been dead six months. No one at the telegraph bureau knew about him. I had never told anyone. Not about the bankruptcy. Not about the rope. Not about the letter he had left on the kitchen table, the last words he had written to my mother before he hanged himself from the beam in our attic room.

I pressed the key: WHAT DO YOU WANT?

I want you to test me, the machine clicked. If I am innocent, you must help me. If I am a murderer, you must call the constables. But you must know which one I am first.

This was madness. It had to be a prank—some junior clerk in the reading room playing a cruel joke on the night woman who sat alone in the dark. But the words kept coming, and they kept getting more specific.

Your father's letter said: Eleanor, I am sorry I could not keep what I promised. Forgive me. He wrote this three days before he died. He wore a grey coat with a torn button on the left sleeve. The rope was from the garden shed.

I could not speak. The fog outside was so thick I could not see the desk in front of me. I pressed the key: WHO ARE YOU?

My name is Arthur Blackwood. I work at the Cold Storage on Wapping. And three nights ago, a man came to me with a body.

I pressed the key: What body?

A nobleman. Lord Ashworth. He had been beaten and cut apart. The man who brought him said he did it himself—that Ashworth had abused servants for thirty years and no one would ever miss him. The man said he felt no joy in it, only a terrible necessity. He asked me to store the body in the coldest chamber and never speak of it.

I pressed the key: And you agreed?

I agreed because I did not know what else to do. I am not a brave man. I am just a man who keeps ice in boxes and watches the fog come in from the river.

The machine clicked for a very long time. When it spoke again, the words came slowly, as if the person on the other end was crying while typing.

I do not know if you believe me. I do not believe myself. But I called you because I need someone to know. Someone to witness. If I am guilty, I need someone to know that I am guilty. If I am not guilty—if I am just a man who found a body and did not know what to do—then I need someone to know that too.

I sat in the dark and thought about my father. I thought about the rope and the letter and the way the attic room smelled of dust and old grief. I thought about how no one had known about any of it until tonight. Until a machine in a Cold Storage station on Wapping decided that someone needed to know.

I pressed the key: I am afraid to tell you my name.

The machine clicked. Once. Twice. Three times.

So am I, it said.

The fog pressed against the windows. The telegraph machine sat between us like an altar. I thought about putting on my black cloak. I thought about walking through the fog to Wapping. I thought about finding Arthur Blackwood and looking into his eyes and knowing whether he was a murderer or a witness or something in between.

I threaded a fresh strip of paper through the roller.

We are both human, I wrote. That has to be enough.

The machine clicked one final message. Then the paper feed stopped. The room was silent except for the fog settling against the glass.

I put on my cloak. I took the lantern from the hook by the door. I stepped out into the street and into the fog, and the fog took me in like a mouth, and I did not know if I would find the Cold Storage station, or if I would find anything at all once I got there.

But I walked anyway. Because someone had to know. And because, for the first time in six months, I did not feel entirely alone in the dark.