In this inventive romantic thriller, Del has the power to navigate between alternate realities—and the power to save multiple worlds. Every time someone makes a choice, a new, parallel world is spun off the existing one. Del knows this because she’s a Walker, someone who can navigate between the worlds, and whose job is to keep the dimensions in harmony. But after she has been forbidden from Walking after a training session goes horribly wrong, she secretly starts to investigate other dissonant worlds. She’s particularly intrigued by the echo versions of Simon Lane, a guy who won’t give her the time of day in the main world, but whose alternate selves are uniquely interested. But falling for Simon draws Del closer to a truth that the Council of Walkers is trying to hide—a secret that threatens the fate of the entire multiverse.