They weren't panic attacks. Of that much, Kate is certain, no matter what the shrink said. But it's even harder to accept the explanation offered by her grandmother—that Kate is reacting to temporal distortions only she can feel, thanks to designer DNA inherited from her time-traveling ancestors. Kate suspects this tale is the result of her grandmother's brain tumor until reality shifts before her very eyes. Her trigonometry teacher morphs into someone else entirely and a stranger sits in her assigned chair, which was empty the second before. This reality sucks, with the sole exception of meeting Trey, the new guy in her trig seat. Despite overwhelming evidence to the contrary, he doesn't seem to think she's crazy. With Trey's help, Kate learns her grandmother was murdered during research at the 1893 Columbian Exposition. Her mom was never born and her dad is now someone else's dad. Strangers on the Metro blink in and out like fireflies, including a guy with dark, haunted eyes who claims he knew Kate intimately in a reality she can't remember. Then there are the Cyrists, a group that shouldn't even exist, who are planning to launch a very drastic form of environmental defense.If not for the odd blue medallion, Kate would simply cease to be. And if she cannot learn to use that medallion to prevent her grandmother's murder at the Expo, billions of people will meet an identical fate at the hands of the Cyrists. With so many lives on the line, Kate has no choice. But changing the timeline is not without cost. Kate will remember the past few months with Trey, but when he looks at her, he'll see a total stranger.