This series was set in a fictional Yorkshire town and based on the books by David Nobbs, the creator of Reginald Perrin and Henry Pratt. Each episode took place at a different social function (a "do") and followed the changing lives of two families, the working-class Simcocks and the middle-class Rodenhursts, together with their respective friends, Rodney and Betty Sillitoe, and Neville Badger.

A British Sub goes missing at the end of the war leaving only one crew member surviving. Everyone believes it lost to the bottom of the Baltic Sea, then 40 years later it reappears without a crew. The British government send for the the surviving crew member (David Jason) now a marine biologist. With a new crew and Jason then proceed to trace the last know happenings on the sub. But this submarine has a life of its own and the new crew soon start showing characteristics of the old crew.