The main strand of this episode uses a well-worn plot idea: a group of friends meet regularly for weekends of drinking, horse-play, and childish games in an attempt to amuse themselves and escape the dreariness of day-to-day life, but beneath the surface are rivalries, jealousies, animosity, and personal inner tragedy.
Onto this strand is grafted one in which Mairgret tries to investigate a murder without a body, based on tantalizing information from a man convicted of another murder.
The problem is that the group-of-debauchees idea is very difficult to make plausible unless they are either upper-class rebels of the 1920s or teenage tearaways of the lower orders. In either case, they need to be convincingly young. The group in this story don't fit believably into any recognizable social stratum and are patently middle aged. Consequently the potential motives for murder as presented are hard to believe in and the general air of the episode is a curious mixture of silliness, flatness, and pretentiousness.
There is an interesting sequence of film at a race track which was bold for the time and context but goes on too long to sustain interest due to the (necessary) fixed-camera single-shot approach.
Frank Williams, in a very small part, doesn't actually say "Well reeee-ally !" but one expects him to at any moment and in every other respect he was clearly destined to take up the living of St Anselm's, Warmington-on-Sea.
And a spotting opportunity for Dr Who watchers is veteran Dalek John Scott Martin as an extra in arab getup.