When twins Didi and Flow move to South London after their parents' sudden disappearance, nothing prepares them for their first day at the Sun School — a place that transforms into a giant yellow cake, where teachers behave like they're under a spell and only children notice the strangeness. With the help of another pair of twins, Joan and Joe, they begin to uncover a series of bizarre clues that hint at something much bigger and darker beneath the school itself. With the grown-ups oblivious and time running out, the twin-twins must fix things — before the world changes forever.