Wages of Sin

In the early part of the 21st Century disaster struck -an experiment on an orbiting station went wrong -bad wrong. The Accident almost destroyed the universe, and ripples in time washed over the Earth. Like the plagues of an earlier millineum, Earth was depopulated, and then it rebuilt. And the people of the post-disaster world learned that things were going to be a little different. They'd be able to travel into the past, utilizing remnant time strings. It took brave pioneers to map the time string gates. It turns out that if you aren't extremely careful, you can zap yourself out of existence with a careless jump. So elaborate rules are evolved, and Time Travel stations have become big business.