Twelve-year old twins, Mika and Ellie, live in a future behind a
wall - safe from the plague animals beyond. Or so they've been told.

But when one of them disappears, and the other takes part in a sinister
virtual reality game, they begin to discover their concrete
world is built on lies. As they go in search of the truth, and
a strange sound in their heads grows to a roar, they find out that
children and the planet have never mattered more.