An adaptation of Raymond Briggs' children's classic that mixes live action and CGI animation to follow the adventures of a family of green monsters who live in the slimy underground world of Bogeydom. Fungus and his wife Mildew suspect their son Mould is illicitly dabbling in human culture, sparking a family argument that sees the boy flee to the surface. Above ground in Daventry, Daryl Hedge's go-getting wife Wendy won't let him forget it that he is unemployed, while his daughter Lucy has fallen for a disagreeable older boy called Dean..