IT WAS a dry, cold evening in November when the old man turned up at the television studio. He walked in, looked around, hung his jacket on a chair, and made himself at home.

His hair was white and soft, like a professor's or a prophet's. He was perhaps 70 years old, with fat gathering round his waist. Behind the large horn-rimmed glasses the eyes were kind, but challenging. Strangely, though the studio lights burned hot as Africa, he wore his shirt buttoned tight about his neck.

“Hot in here,” he remarked to a young man with a clipboard, as a camera slid by. “I should lose my tie.”

With his eyes shut, he unbuttoned his shirt, slowly.

The young man, and the camera, stopped.

Beneath the old man's shirt was an illustration of a forest, something like a coloured tattoo. But the forest moved. The giant ferns and trees of prehistory crowded in on a silver path that hovered six inches above the ground. Men were walking along it, tourists on a Time safari, out to kill dinosaurs. A hunter called Eckels blundered off the path into deep moss, and later found a butterfly, glistening green and gold and black, embedded in the mud on his boot. Because of that dead butterfly history changed, in a whisper or a roar, all down the aeons of time. The tale was called “A Sound of Thunder”.

“Want to see more?” the old man asked.

The young man nodded.

On the old man's pale, plump back was a painted library of books. A small boy, recognisably himself, ran in and filled his eager arms with Oz books and Tarzan stories. A pile of Buck Rogers comics lay on the floor. He seized them and began, carefully, to cut out the coloured strips. The small boy grew, the books changing round him, until he was in the basement of UCLA's Powell Library in Los Angeles, 30 years old, banging on a rented typewriter. Beside him lay copies of magazines with his stories inside. But now the crammed shelves had begun to glow. A strange, acrid smell crept in the air. A fireman called Montag was spraying the room with kerosene, laughing grimly. Then with a flick of his igniter he lit a gorging fire that turned the evening sky red and yellow and black. Pigeon-winged books died on the ground, their pages lifting like feathers, until, at Fahrenheit 451, they burst into flame. In this world reading and thinking had been banned. Literature and philosophy survived only in men's heads.

The young man, wide-eyed, asked whether this was a prediction. No, said the old man. It was a warning. His task as a science-fiction writer was to imagine problems, to prick thumbs. But it was also to offer hope. He had foreseen mobile telecoms, iPods, wall-to-wall TV, talking trains and pedestrians arrested for walking the streets at night, but none of it was meant to spread unhappiness. He loved that fragile, rare, extraordinary thing called life, and wanted man to keep blowing on the coals of the universal wilderness and mystery that surrounded him.

Silent, the young man nodded. But his eyes strayed to the old man's neck, where Terrors lurked at the top of the stairs, and to his right shoulder, where huge green wings were growing, and to the ends of his white hair, in which a wind blew that keened with the voices of everyone it had killed.

“Here's one that will really interest you,” said the old man.

His forearm showed a scene in Waukegan, Illinois, where he was born. White palings, apple trees, front porches, and a hill strewn with dandelions, his special flowers. When the Apollo 15 astronauts wanted to name their lunar landscape after him, they fixed on Dandelion Crater.

A boy of 12 was racing down the hill. He burst into a fairground tent and there, before him, was Mr Electrico in his chair, with a sparking sword. He froze. Mr Electrico tapped him on the brow and cried, “Live for ever!”

“But who can live for ever?” asked the old man.

He opened his palm.

Inside it was a fire lantern, glowing gently through its paper shell. On every Fourth of July he and the grown-ups would release these gossamer spirits, blue, white and red. Their beauty as they rose through the night sky made him cry about the end of things. Now another floated up, a blue sphere, and hovered over a landscape of delicate ruined cities and fossil seas. Silver rockets, discarded by American colonisers, twinkled on the distant hills.

This, the old man explained, was Mars, and the blue globes were the disembodied souls and intellects of Martians who had lived long ago. These gentle, musical beings, with their golden eyes, would never trouble the brash new arrivals who, in his “Martian Chronicles”, were bringing in rocket-loads of Oregon pine to build towns much like Waukegan. But they and their soft, sad voices would continue to haunt both Mars and Earth as long as men were there to imagine them—or become them.

The old man sighed. The Illustrations had tired him. So many characters running, weeping, staring, talking, all the years of his writing life. Five hundred stories.

He buttoned his shirt collar, shook hands with the young man, and left.

In the empty street, another blue sphere glimmered and rose…