Time's echo
(Book)

"Kiernan Dunne abandoned his family ties to help Kate fight the Cyrists, and he's never regretted that for one moment. But he doesn't understand why Kate can't remember that night in 1893 Chicago, when she turned back to face the killer chasing them through the smoky corridors of the World's Fair Hotel. Kate placed the CHRONOS key around his neck and made his eight year old self promise to wear it always, and that's a promise Kiernan has never broken. When Kate suddenly vanishes after a Cyrist-engineered time shift, that hidden medallion is Kiernan's only hope for finding her. He returns to the Cyrist fold to look for clues, but his search will lead him back to the question that has haunted him for years - what really happened after he left Kate at the World's Fair Hotel?"--Publisher's description.