Some decisions have unimaginable consequences. Every time someone makes a choice, a new parallel world is spun off the existing one. Eating breakfast or skipping it, sneaking out instead of staying in bed—every decision creates an alternate universe in which an Echo self takes the road not traveled. As a Walker who can navigate between these realities, Del is training to help keep the dimensions in harmony. When Del secretly starts to investigate other dissonant worlds, she get tangled up with an Echo of her longtime crush. She knows she shouldn't keep seeing him. But as Del persists, she uncovers a truth that the Council of Walkers is trying to hide—a secret that threatens the entire multiverse.