A young boy and his grandmother face off against real witches — creatures who despise children and plot to eliminate them. When the boy accidentally encounters a coven of witches at a seaside hotel, he learns of their sinister plan: the Grand High Witch has invented a potion that will turn all children into mice. After being turned into a mouse himself, the boy and his grandmother must use their wits and bravery to stop the witches and save children everywhere.