April and Sam meet in the hospital on the day they're born and become friends. Years later, they have forgotten their original encounter, but they both feel that something is missing from their lives.
One day, without knowing why, April blows a kiss to a passing breeze. This breeze, like all winds, has travelled between the worlds, and knows that April and Sam will one day be the rulers of a fantastic land called Echo.
The breeze delivers the kiss to Sam, who sets off to find his missing friend, though he can't remember anything about her. But instead of April, Sam meets a band of half-real wanderers led by the half-real magician, Jodicus Krem. Krem thinks Sam can help him become entirely real again.
Krem explains that Sam is an Imagifex. His imagination is so strong that he can take something half real and bring it the rest of the way to reality. Sam agrees to help him in exchange for help finding his missing friend.
April meanwhile has distracted herself with her dream of being an inventor. She longs to craft machines that can change the world. But her mother believes she's too young for batteries and wires. So April can only create her devices on paper.
April is surprised when a boat she designed and never built appears in her bedroom. That's when Sam shows up, claiming he can make all her inventions real.
April and Sam climb aboard the boat, which they name the Ziroo. As they sail, they create the world of Echo, where music boxes fly like finches, clouds walk on stilts, and buildings sing to each other in the evening like crickets. Finally, they build bridges to the everyday world and invite Sam's half-real friends to come to Echo.
But someone crosses who was never invited: Jodicus Krem. Upset that Sam hasn't fulfilled his part of the bargain, Krem goes into hiding in the dark corners of Echo and begins to turn the world against its makers.