Every time someone makes a choice, a new, parallel world is spun off 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 alternate universes in which echo selves take the roads not traveled. 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 Del's decisions have consequences too. Even though she's 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.

"O'Rourke brilliantly builds an intricate and complex alternate science-fiction universe that contains beautiful imagery and visualization. A definite page-turner." --School Library Journal