Internal evidence suggests very strongly that this was originally intended to be the last-ever segment of the long-running "Inspector Morse" series. The question of Morse's retirement (and also that of Chief Superintendent Strange) is raised several times; the episode went out ten years after the series began; viewers finally learn Morse's first name; and, to clinch matters, he finally gets himself a girl-friend who loves him back and doesn't turn out to be a criminal of some sort, or to get murdered.
The trivia items below may give away important plot points.
In this episode, Morse's first name is revealed to be Endeavour. He was named after James Cook's vessel HM Bark Endeavour. Morse mentions that his mother was a Quaker, who have a tradition of "virtue names", and his father was a fan of Captain Cook.