Jack (Asa Butterfield)'s grandfather often told him bedtime stories when he was a child. There were many children with special abilities in the stories. After his grandfather died mysteriously, he left clues about the mysteries of this world in another time and space. Following these clues, Jack entered this mysterious world and found that these strange children really existed. They lived here to avoid terrible mutant monsters. With Jack's arrival, danger also arrived. Jack needs to fight against the dark forces together with these children.