Time's Edge (The Chronos Files, 2)

To stop her sadistic grandfather, Saul, and his band of time travelers from rewriting history, Kate must race to retrieve the CHRONOS keys before they fall into the Cyrists' hands. If she jumps back in time and pulls the wrong key--one that might tip off the Cyrists to her strategy--her whole plan could come crashing down, jeopardizing the future of millions of innocent people. Kate's only ally is Kiernan, who also carries the time-traveling gene. But their growing bond threatens everything Kate is trying to rebuild with Trey, her boyfriend who can't remember the relationship she can't forget.

As evidence of Saul's twisted mind builds, Kate's missions become more complex, blurring the line between good and evil. Which of the people Saul plans to sacrifice in the past can she and Kiernan save without risking their ultimate goal--or their own lives?