Otherworldly creature Mirabelle, whose human form appears about twelve years old, lives with a diverse group of monsters at the House of Rookhaven near an English village. After the end of World War II, orphaned siblings Jem and sickly Tom arrive at Rookhaven, making the monsters aware for the first time that there's a tear in the Glamour, the barrier created as a truce with the nearby humans and to protect them from other monsters who want to harm them. Mirabelle and the family soon learn something is after them, a monster is on the loose, and they need to protect themselves while trying to keep peace with the local village.