When they passed through the hall air lock, they were met by a hot wind blowing dusty air.

“There’s my boy!” Shi Qiang shouted, pointing at a man bounding up the steps. From this distance, Luo Ji could make out only that the man was in his forties, so he was a little surprised at Shi Qiang’s certainty. As Shi Qiang hurried down the stairs to welcome his son, Luo Ji turned his eyes from the reunion to the surface world before him.

The sky was yellow. He now realized why the image of the sky showing in the underground city was shot from a height of ten thousand meters, because, from the ground, the sun was only visible as a hazy outline. Sand covered everything on the ground, and cars passed by on the streets dragging dusty tails. It was another sight from the past for Luo Ji: cars that traveled on the ground. They didn’t seem to run on gasoline. They came in all kinds of weird shapes, and some were new and some old, but they all shared one feature: Every car had a flat sheet installed on the roof, like an awning. Across the street, he saw an old-era building with sand-covered windowsills and windows that were either boarded up or glassless black holes. However, people were evidently living in some of the rooms, because he saw clothing hanging outside to dry and even some potted flowers on the windowsills. Though the airborne sand and dust kept visibility low, he soon located a couple of familiar building outlines farther away and knew for certain that he was in the same city where he had spent half his life two centuries ago.

He walked down the steps to the two men who were hugging and pounding each other in their excitement. Seeing the middle-aged man up close, he knew that Shi Qiang hadn’t made a mistake.

“Dad, when you figure it, I’m only five years younger than you,” Shi Xiaoming said, wiping tears from the corners of his eyes.

“Not bad, kiddo. I was afraid some damn white-bearded old man would be calling me Dad,” Shi Qiang said with a chuckle. Then he introduced Luo Ji to his son.

“Oh, Dr. Luo. You used to be world famous,” Shi Xiaoming said, as he looked Luo Ji up and down.

The three of them headed toward Shi Xiaoming’s car, which was parked at the side of the road. Before they got in, Luo Ji asked about the thing on the roof.

“It’s an antenna. Up on the surface, we have to use whatever electricity leaks through from the underground city, so the antennas are a little larger, and the power is only enough to run the cars on the ground. They can’t fly.”

The car wasn’t fast, due either to the power or the sand on the road. Luo Ji looked out the window at the sandy city. He had a belly full of questions, but Shi Xiaoming and his father kept talking and he couldn’t get a word in.