Tom Calloway learned to walk again in a Philadelphia hospital, and learned to breathe again in a Pittsburgh smog cloud that tasted of iron and bad decisions. He did not learn to stop coughing. The gas at Passchendaele had carved channels through his bronchial tubes, and the doctors called it a "manageable condition." Manageable meant he could stand upright, sit at a desk, and pretend he was a functioning adult. It did not mean he could run up stairs without thinking his heart would split his chest open.

J.P. Harriman found him through a mutual acquaintance at a club off Liberty Avenue where the jazz played loud enough to drown out everything but the drinks. Harriman wore a suit that cost more than Tom's entire war pension. He had a face like a bank vault—solid, unyielding, designed to keep things in and everything else out.

"I need someone to transport a shipment," Harriman said, not wasting time on weather or the war or any of the small talk men used to bridge the gap between strangers. "A sample. Industrial. You carry it from my office downtown to the university lab in the East End. Then you carry it back. That is the job. Five hundred dollars."

Tom looked at the man. Five hundred dollars in 1922 was not pocket change. It was a house payment. It was a future. It was a man who didn't care about the war, didn't care about gas lungs, didn't care about anything except the geometry of his own balance sheet.

"What kind of sample?" Tom said.

Harriman opened a leather briefcase. Inside sat a lead-lined box about the size of a loaf of bread. He did not open it. He did not need to.

"Radium," he said. "A new ore from Colorado. My chemists tell me it has properties that could revolutionize industrial processes. I need a control sample transported safely. Lead-lined container. You don't open it. You don't set it down for more than necessary. You deliver it."

Tom laughed. He did not mean to, but it came out anyway—a dry, rattling sound that set his chest on fire. "Radium. You want me to carry radium."

"I want you to carry it in a lead container," Harriman said. "It is perfectly safe."

Tom took the job. He told himself it was the money. He told himself it was pride—here was a man who needed him for something, however briefly. He did not tell himself that the war had already taken everything he had to lose, and that five hundred dollars was the only thing standing between him and a room above a saloon where the landlady stopped leaving water on his doorstep after the third week.

The first delivery took him from Harriman's steel empire downtown, through streets lined with men whose shirts were as black as the smog, to the university where a Dr. Miriam Sato waited with clipboards and a quiet intensity that reminded him of nurses at the front. She opened the container with gloved hands, extracted a small vial of substance that glowed faintly blue in the dark, and placed it under a glass apparatus.

"Come back in three hours," she said. "Bring it back to Mr. Harriman."

Tom carried the vial in the lead box through the Pittsburgh evening, feeling nothing different except the weight of the case against his ribs. He slept in his room above the saloon and dreamed of fields in Flanders that glowed the same blue as the substance in the box.

On the third delivery, Dr. Sato kept him. She showed him slides under a microscope—cells, she said, cancer cells. She had exposed some of them to the radium. The cells had died. All of them.

"It is lethal to malignant tissue," she said, and there was something in her voice—reverence, terror, both. "Tom, this could cure cancer."

Tom looked at the slides. He thought of the men in his platoon who had gone home with holes in their legs and their lungs and their faces, and who were now dying slowly in boarding houses because the war had ended and nobody cared about them anymore.

"Harriman knows this?" he said.

Dr. Sato hesitated. "Mr. Harriman has funded my research. He is—ambitious. He sees the industrial applications. The luminous paint, the new processes. He has not been interested in the medical implications."

Tom carried the box back to Harriman's office. The magnate did not ask about the medical applications. He asked about the delivery time. He asked about the weight. He asked if the container had been compromised. He did not ask if Tom was all right. Tom was not. His gums were bleeding when he brushed his teeth. A small spot on his forearm had turned gray and would not heal. He told nobody.

He continued the deliveries for six months. He stopped sleeping above the saloon and moved into a small apartment near the river, where the water ran colors that no river should run and the men who worked there came home with their skin peeling off in sheets. He told himself he was doing it for the money. He bought a new coat. He bought shoes that did not have holes. He told a woman at a café named Clara that he was working in logistics. She believed him. She was kind. She did not stay.

In the seventh month, Dr. Sato called him to the lab at midnight. She was trembling.

"I ran more tests," she said. "Tom, the radium—it is not just lethal to cancer cells. It is curative. I have seen tumors shrink in tissue samples. I have seen—Tom, this is the most important discovery of the century."

"Where is the sample?" Tom said.

"In storage. Mr. Harriman has increased security. He knows what we are doing now. His chemists have told him." She paused. "He wants to patent it. He wants to control the production. He does not want to give it away."

Tom stood in the lab and looked at the blue glow from behind the glass. It was beautiful. It was killing him. It could save millions.

"What does he want from me?" he said.

Dr. Sato was quiet for a long time. "He wants you to stop coming here. He has—arranged for your compensation. A monthly stipend. He says your role is complete."

Tom thought about the stipend. He thought about his coughing. He thought about the gray spot on his arm, which had grown to the size of a quarter and pulsed with a dull pain that reminded him, constantly, of the thing eating him from the inside. He thought of Clara, who had left because he smelled like a hospital and talked in his sleep about men who had no legs.

"Tell me what to do," he said.

Dr. Sato gave him a small vial—pure radium chloride, sealed in glass, wrapped in lead foil. "Take this," she said. "Carry it. Let him think you are still his courier. But I will need you close. When the time is right, you will testify. You will bring the evidence to Washington."

"The time is right" came sooner than Tom expected. Harriman, confident in his control, began presenting the radium to investors. He spoke of luminous paint and industrial processes and the future of energy. He did not speak of cancer. He did not speak of the men in Pittsburgh whose skin was falling off. He did not speak of Tom, or of the gray spot that had spread across his chest like a map of the places he had never been able to go.

The hearing in Washington was small. A senator from Ohio, two committee members, a stenographer who typed with her fingers like a pianist. Tom stood at the podium with the lead box on the table before him. His gums were bleeding—he could taste the iron, and he wondered if it was from his mouth or from the radium, or from both. He opened the box. The vial glowed blue in the fluorescent light.

"This substance," Tom said, his voice thin and raw, "is killing me. It is killing the men in Pittsburgh. It is curing cancer. And J.P. Harriman knows it, and he is choosing to sell paint instead of saving lives."

The senator leaned forward. "Mr. Calloway, do you have evidence of that?"

Tom looked at the vial. It glowed. It killed. It healed. It was the most beautiful and terrible thing he had ever held.

"Yes, Senator," he said. "I am the evidence."

He did not live to see the hearings conclude. The radiation had moved too far by then—he could feel it in his bones, in the marrow, eating the last of the man he had been. Dr. Sato sat beside him in the Washington hotel room while he slept, which was most of the time now, and read him articles about the hearings, about the outrage, about the new regulations that would force disclosure of radium's medical applications.

"You did it," she said, on the night he stopped sleeping and started watching the ceiling.

Tom looked at the ceiling. It was white and cracked and beautiful. "I carried a box," he said. "That is not— that is not doing anything. That is just—" He coughed, and it hurt, and it always hurt now, but he kept going. "That is just carrying a box."

"Sometimes that is enough," Dr. Sato said.

Tom thought about the men in Passchendaele. He thought about Clara. He thought about the blue glow. He thought about the weight of the lead box against his ribs, and how for seven months, every day, he had picked it up and carried it from one place to another, and how that simple act—carrying, enduring, refusing to set it down—had been the only heroic thing he had ever done.

"Maybe," he said. And then he closed his eyes, and the blue glow filled the room, and the room filled with the faces of all the men he had known, and none of them were asking him to carry anything anymore.