The village of Aberbryncraig is rocked by Dai News, the fussy owner of the newsagents and sweetshop in the High Street and vendor of the legendary Neptune Bars, and especially by his cries of anguish when he is missing some Neptune Bars and suspects they have been stolen.
Mrs Mopalot (Mrs Branywn Jenkins) is intrigued and persuades her husband, Idwall (he hates being called Mr Mopalot and no one dares do so), to discuss theories of where the Neptune Bars may be going. This causes many bedroom disasters as they debate in bed, a disaster even including a cocoa shower.
Mrs M cleans for everyone, so she is in a good position to find out information and get it deciphered. The villagers stick together as they usually do. There is romance in the air as the mystery is finally solved and celebrated at the famous Aberbryncraig summer party.