“The last time I gave someone a piggyback,” he says, “was twenty-three years before you were born. The Spoke was still under construction then. I’ve never been up to the top either.”

She straddles his back, puts her arms around the plasteel of his neck. He rises fluidly to his full height. The first step lights up when he steps on it—and the second, and the third. He bounds up them in an accelerating series of white pulses.

“How old are you?” she asks.

“I came online one hundred and sixteen years ago, almost a century before your own operating system began to function.”

“Ha.” They’re moving so fast now that it makes her feel queasy. Her Monowheel doesn’t go this fast at top speed. He leaps three steps at a time, keeping a steady, jolting rhythm. Iris cannot bear to look over the glass retaining wall on her right, cannot look at the black nautilus swirl of steps below them. For a while she is silent, eyes squeezed shut, pressing herself into his back.

Finally, just to be talking, she asks, “Who was the first person to put a coin in your meter?”

“A boy named Jamie. We were close for almost four years. He used to visit me once a week.”

“That’s where the money is,” she says. “My dad had repeat clients, too. There was a woman who used to cut his throat every Sunday at one. She bled him dry, and he did the same to her—took her for every cent she had. How much did you squeeze good old Jamie for before he got bored of you?”

“He didn’t get bored. He died, when malware infected his enhanced immune system. He raved about cheap Viagra and Asian women who want English-speaking husbands for two awful days before the infection killed him. He was thirteen.”

She shivers, has heard horror stories about corrupted bioware. “Awful.”

“The price of being alive is that someday you aren’t.”

“Yeah. My meter is running, too. Isn’t that the whole point of birthdays? To remind you the meter is running down? Someday I’ll be dead, and you’ll still be making new friends. Carrying other girls up other stairways.” She laughs humorlessly.

“However old I myself may be, consider that in a very real sense my own life happens one token at a time, and there are sometimes days, or even weeks, between periods of activity. I’ve outlived Jamie by a hundred and three years in one sense. In another he spent far more time doing and being. And in still another sense, I’ve never lived at all—at least if we agree that life means personal initiative and choice.”