The Invisibles by Susie Bower

A magical kingdom. Four friends. One terrible mistake...

In the Land of Magic, four friends live a life filled with wonder. But there's one rule they must not break: never set foot on the Island of Darkness. So, when one child does the unthinkable, they must all pay a terrible price - exile to Wasteland, the bleak world where only grown-ups live.

For Grace, this fate is particularly cruel. She wakes up with no memory of her magical home, or how she ended up here - and the only clue to her past is guarded by two hostile and mysteriously invisible children.

As Grace uncovers the Invisibles' secrets, she must work out a way to return home, before Wasteland traps her forever...