Ignored in her own house, Lily Carter watches her parents pour all their attention into her autistic sister, Grace. So when she insists there’s a mysterious couple on the other side of the mirror, nobody takes her seriously. But the version of family she finds in that reflected world is gentle, caring, and full of the belonging she never gets at home. Starved of love in the real world, Lily becomes increasingly attached to the mirror family, and the line between wishful thinking and reality begins to blur.