The shelling at the Somme had taken Thomas Harrington's left arm at the elbow, and it had taken something else he could not name—something that made the silence after the guns sound louder than the guns themselves. He came home to Cornwall in the autumn of 1919 with a wooden prosthetic and a letter of discharge that felt like a death warrant.

His sister Catherine was twenty-two and fading. The doctors in London called it "asthenic neuritis." Catherine called it the grey—because that is what the edges of her vision were turning into, a slow grey encroachment that ate the world from the margins inward. She sat by the window in their mother's old house and watched the sea and did not speak much.

Thomas found the lighthouse keeper on a Tuesday, following a trail of absurd claims through the local pub. The man's name was Arthur Blackwood, and he had been an astronomer at the Royal Observatory before his colleagues decided that a man who claimed he could light the sun was not fit to chart the stars.

Arthur was seventy-two, bent like a question mark, and his eyes were the colour of sea glass. He lived in a lighthouse on the westernmost point of Cornwall, surrounded by books on celestial mechanics and a collection of whale teeth that he said were "unfinished rockets."

"You want to light the sun," Arthur said when Thomas explained why he had come. He was not mocking. He sounded almost interested.

"I want to save my sister," Thomas said. "You say you can light the sun. Can you not?"

Arthur laughed—a dry, rattling sound. "Light the sun? No. No, I cannot. But I can teach you something almost as useful."

He spent three months teaching Thomas. They built rockets from whale teeth and gunpowder that never left the ground. They charted constellations from a book so old the pages crumbled when Thomas turned them. Arthur told him stories of climbing to the moon on a rope pulled by a whalebone arrow, of steering a crescent moon like a boat through a sea of stars that chimed like wind chimes when they touched the hull.

"You know," Arthur said one evening as they sat on the lighthouse balcony watching the stars come out, "when I was a young man, I really believed it. I believed that if we could just figure out the right combination of powder and angle and star position, we could light the sun. And then the war came, and I shipped out, and I saw men die in trenches so deep that the sky looked like a thin blue line above them. And I thought: what is the point of lighting the sun if men will spend their lives in holes in the ground?"

Thomas did not have an answer. He had lost his arm. He did not feel qualified to answer questions about the meaning of light.

The turning point came in January. Catherine's grey had reached her hands. She could no longer hold a teacup without spilling. Thomas sat by her bedside every evening and held her hand with his right hand and his wooden prosthetic, and she would squeeze both when he told her about Arthur's stories.

"She sounds like a wonderful woman, your Catherine," Arthur said one evening, and Thomas realized the old man was crying. Not dramatically—just a slow leaking of tears that he pretended not to notice. "She reminds me of my sister. She died in the influenza. 1918. I was supposed to visit her. I was charting a comet. I told myself it was more important."

Thomas looked at the stars. They were bright that night, sharp as ice crystals.

"I built a rocket once," Arthur said quietly. "Before the war. A real one. Whale tooth, black powder, a sail. I launched it from this very cliff. It went up—higher than any man-made thing had gone before—and then it fell into the sea and I never saw it again. But for those few seconds, it was flying. And I thought: that is enough. That is all any of us gets. A few seconds of flying."

Thomas went home and sat with Catherine for a long time. Then he went to the local pub and told Captain James Whitfield, his former trench-mate and now a newspaper editor, about Arthur. He told him about the whale-tooth rockets and the stories of climbing to the moon and the old man's single rocket that had flown for a few seconds before falling into the sea.

Whitfield listened and then said, "You know, there are thousands of men coming home from the war with nothing. No arms, no futures, no reason to get up in the morning. They don't need the sun lit. They need someone to remind them that flying—even for a few seconds—is worth something."

Thomas looked at him. "What are you saying?"

"I'm saying you're a fool," Whitfield said affectionately. "But you're a fool with a purpose. Start something. Call it what you want. A club, a society, a gathering. Give these men somewhere to go where they can hear stories about things that fly."

Thomas started the Starlight Society in February. He rented a room above Whitfield's newspaper office. He invited any man who had served—any man who came home with holes in him that the doctors could not name. Arthur came to the first meeting, and he told them his stories. He told them about the whale-tooth rockets and the moon boat and the stars that chimed. The men sat in silence, and when Arthur finished, no one spoke for a full minute. Then a man named George, who had lost both legs at Ypres, said quietly: "Tell us again about the stars that sing."

And Arthur told them again.

Catherine's grey did not recede. The doctors had no treatment for it, and Arthur had no star to wipe. But she began to attend the meetings. She sat in the front row and listened to Arthur's stories with her head tilted back and her eyes wide, and for an hour each week, the grey stopped encroaching.

One evening in March, Thomas found her by the window. She was holding a book—Arthur's old celestial mechanics text, the one with the crumbling pages.

"Arthur told me about his rocket," she said. "The one that flew for a few seconds before it fell. He said it was enough."

Thomas sat beside her. "Do you think it was?"

She looked at him with eyes that were still grey at the edges but bright in the centre. "He flew for a few seconds, Thomas. That is more than most of us get."

Thomas went to the lighthouse the next morning. Arthur was on the balcony, looking at the sea. Thomas climbed the stairs and stood beside him.

"I'm staying," Thomas said. "I'm not leaving Cornwall. I'm going to keep the Society going, and I'm going to help the men, and I'm going to—"

"You don't have to stay," Arthur said. But he was smiling, and his sea-glass eyes were bright.

"I know," Thomas said. And he meant it.

That night, the Starlight Society met for the last time. Arthur was too ill to come, so Thomas told his stories instead. He told them about the whale-tooth rockets and the moon boat and the stars that chimed. He told them about Arthur's rocket that had flown for a few seconds before falling into the sea.

When he finished, the room was silent. Then George, the man without legs, began to clap. Slowly, one by one, the other men joined him. Thomas stood in the centre of the room with his wooden arm and his empty right sleeve and felt something he had not felt since the shelling at the Somme.

He felt the sun rising inside his chest.

It was not a real sun. It was not a whale-tooth rocket or a crescent moon or a star that chimed. It was smaller than that and more real. It was the warmth that spread through the room like light, and it was enough.