Ada and her parents have moved from the city to a small town for her mum's new job. But when they arrive, it's obvious to Ada that something is not quite right. On her newspaper round, she discovers the Banished, magical people who have been exiled from the town by the sinister mayor.

The Banished are trapped behind an invisible shield which means they can't enter the town or see their loved ones. But somehow, Ada can see the shield as a wall of fog and, not only that, she can enter the world of the Banished.