Jeremy and Julian Lewis, dubbed the "Lewis Twins," are two misbehaving brothers who terrorize the city of Swansea from their trailer park home. When their father, Fatty, gets hurt while working on a roof for local kingpin Bryn Cartwright, they make a futile attempt to obtain compensation. Thus begins a campaign of terror, which local police officers Terry and Grayo are unprepared to stop due to their involvement in a heroin deal with Cartwright.