When twelve-year-olds Willa and Manny hear of a mysterious animal prowling their town, they are determined to prove it is real. Following the creature into a cave one full moon, they are swept into an alternate, ideal, world one where pollution and conflict have been conquered decades ago and even their own families seem happier. But when they return, no one believes them. So, with a global war looming in their own world, their quest for proof of the Sideways World becomes ever-more urgent, in a nail-biting race against time. And Willa and Manny will have to make an impossible decision: because once you find a perfect world, can you ever leave it behind . . .?