Jeffrey spends his Saturdays working in Mr Prendergast's junk shop. One day, while they are sorting things out, they uncover a mysterious machine. Jeffrey takes it home to see if he can make it work. It turns out to be a joke-producing machine, and an extremely funny one at that! Soon everyone in town wants one of its jokes. Everyone except Mr Jenkinson, that is, the miserable owner of the shop next door. Of course, what Mr Jenkinson really needs to do is get a sense of humour instead of trying to ruin everyone's fun. But who will get the last laugh?