There's something strange behind the basement door...After the tragic death of their father, Emily and Navin move with their mother to the home of her deceased great-grandfather, but the strange house proves to be dangerous. Before long, a sinister creature lures the kids' mum through a door in the basement. Em and Navin, desperate not to lose her, follow her into an underground world inhabited by demons, robots and talking animals. They enlist the help of a small mechanical rabbit named Miskit and together they face the most terrifying monster of alland Em finally has the chance to save someone she loves.