In the near future time travel is possible. Some believe that small modifications in the past can bring them profit or political gain. They are wrong. Modifications of the past lead to disasters in the present. Mason Edwards and his peers at the National Historical Preservation Institute (NHPI), a military backed, government-funded organization, are dedicated to the ideal of zero tolerance for historical tampering. The way it happened the first time is the way it has to stay. When a modification is detected in the past, Mason, or one of his peers, is sent into the past to make things right....