Adaptation of Raymond Briggs' classic tale of Fungus the Bogeyman, who lives with his wife Mildew, and his children mould and mucus in the slimy underground world of Bogeydom.
Fungus' job is to venture above Bogeydom and scare dry-cleaners (a Bogey's name for humans). But on one trip, disaster strikes and a dry-cleaner discovers their existence in Bogeydom. The dry-cleaner Jessica strikes up a friendship with Fungus' children and escapes back home to tell her father George (Martin Clunes) all about it. George then decides to stake out the entrance to Bogeydom, in order to catch a real-life Bogeyman.