Britain, 1940, the world is at war and 10-year-old twins Harry and Rosie are evacuated from London to live with their Great Uncle. The twins immediately miss home and perhaps most of all for Harry, the tearoom where their mum works, and Harry spends hours watching the professional dancers – secretly dreaming of the day he might do the same. Faced with stony silences from their Great Uncle Rupert and endless rainy days in the stormy village of Cotterill Cove, they throw themselves into the local dance show, determined to do their bit for the war effort and maybe even dance at the famous Winter Gardens in Blackpool. But when Harry sees strange flashing lights out on the treacherous mudflats one night, he and Rosie discover their new home is hiding some huge secrets and the enemy is a lot closer than they thought.