Delancy Sullivan has always known there’s more to reality than what people see. Every time someone makes a choice, a new, parallel world branches off from the existing one. Eating breakfast or skipping it, turning left instead of right, sneaking out instead of staying in bed ~ all of these choices create an alternate universe in which an echo self takes the road not travelled and makes the opposite decision. As a Walker, someone who can navigate between these worlds, Del’s job is to keep all of the dimensions in harmony. Normally, Del can hear the dissonant frequency that each world emits as clear as a bell. But when a training session in an off-key world goes horribly wrong, she is forbidden from Walking by the Council. But Del’s not big on following the rules and she secretly starts to investigate these other worlds. Something strange is connecting them and it’s not just her random encounters with echo versions of the guy she likes, Simon Lane. But Del’s decisions have unimaginable consequences and, as she begins to fall for the Echo Simons in each world, she draws closer to a truth that the Council of Walkers is trying to hide ~ a secret that threatens the fate of the entire multiverse