“I’m sorry,” Mahler said, getting up.

He decided to end the interview then and there. He had to get rid of this jumper because there was another space traveler coming right up. Some days they came thick and fast, and this looked like one of the really bad days. But the efficient mechanical tracers never missed a jumper.

“But can’t I live on Earth and stay in this spacesuit?” the man asked, panicky now that he saw his interview with Mahler was coming to an end. “That way I’d be sealed off from contact at all times.”

“Please don’t make this any harder than it is for me,” Mahler said. “I’ve explained to you why we must be absolutely inflexible. There cannot—must not—be any exceptions. Two centuries have now passed since the last outbreak of disease on Earth. So naturally we’ve lost most of the resistance acquired over the countless generations when disease was rampant. I’m risking my life coming so close to you, even with the spacesuit sealing you off.”

Mahler signaled to the tall, powerful guards who were waiting in the corridor, looking like huge, heavily armored beetles in the casings that protected them from infection. This was always the worst moment.

“Look,” Mahler said, frowning with impatience. “You’re a walking death trap. You probably carry enough disease germs to kill half the world. Even a cold—a common cold—would wipe out millions now. Acquired immunity to disease has simply vanished over the past two centuries. It’s no longer needed, with all diseases conquered. But you time travelers show up loaded with potentialities for all the diseases that once wiped out whole populations. And we can’t risk having you stay here with them.”

“But I’d—”

“I know. You’d swear by all that’s holy to you or to me that you’d never leave the confines of the spacesuit. Sorry. The word of the most honorable man doesn’t carry any weight against the safety of two billion human lives. We can’t take the slightest risk by letting you stay on Earth.