In a way, it’s very handy. Go back to fifteenth-century France and you’ll find yourself thinking in the local language and dialect and generally knowing your way around. Only the massive energy link, a lifeline of sorts, between here and there keeps you from being completely absorbed. Unfortunately, the longer you are there, the more energy is required to sustain you. It’s in some way related to the subject’s age, although we haven’t gotten the exact ratio. It requires more energy to send an older person back than a younger. Someone up to about the age of fifty we can generally sustain back there for the number of time-frame days equal to half his age. How old are you?”

“Forty-one,” he told the scientist.

“Yes, so we could safely send you back for a period of twenty days with an adequate safety margin. Over fifty, it accelerates like mad. It’s simply not safe.”

“What happens, then, if you overstay your welcome? Don’t come back within that margin?”

“Then the energy required to retrieve you would exceed our capacity. The line would break. You would literally be integrated into that past time as that created person, eventually with no memories or traces that you were not native to that time and place. And if that was, say, 1820, we could not later rescue you. You could not go forward of your own present—1820—and even if there was a way, we would retrieve someone else, not you. Someone, incidentally, invariably minor and unlikely to change any events. We learned our lesson the hard way.”

“You’ve lost someone, then?”

He nodded, “An expert in Renaissance history and culture, who was also a valuable agent when he attended East European conferences, which is why he was one of the few scholars we allowed to downtime personally. He was forty-six when he went back the first time, and he stayed two weeks. Later, he needed a follow-up, so we sent him back again—and lost him.