That's why we always pretend to be part of the world where we trade. Some alternates are advanced enough that they might be able to use the technology if they got their hands on it. That could be very, very dangerous.” The desktop showed another clip from the world where the Nazis had won the Second World War. It wasn't pretty. Ms. Mouradian went on, “That rule is also why we drill for oil and do our mining on alternates where there are only hunters and gatherers, or else worlds without any people at all. On worlds like those, we don't have to hide.”

On the desktop, oil rigs stood like steel skeletons in the middle of a vast, golden desert. Antelope with enormous horns watched, wondering what the fuss was about. An oil worker in grimy coveralls walked up to one and stroked its nose. It stood there and let him. It had never learned to be afraid of men. In that alternate, there were no men to be afraid of.

The antelope disappeared from the desktop. Jeremy sighed, and he wasn't the only one. Ms. Mouradian said, “Now we're going to go over some of the Supreme Court decisions that center on crosstime travel.” Jeremy sighed again, on a different note. Again, he wasn't the only one.

Amanda Solters stood under the awning at Canoga Park High. She stayed out of the sun while she waited for the bus and for her brother to show up. She hoped Jeremy would get there before the bus did. His last class this year was on the far side of campus, so sometimes he cut things close.

While she waited, she checked her handheld to see what she had to do tonight. She made a face at the thought of algebra homework. That was old-fashioned, boring drill and practice. She had to understand what she was doing to get it right. It wasn't like a foreign language, where she could soak it up in a few sessions with the implant. She'd learned Spanish that way, and French, and neoLatin and classical Latin for trips out to the alternate with her parents and Jeremy.