The government department known as Doomwatch were set up to combat pollution and enviromnental disasters, and they send one of their number, Dr Del Shaw (Ian Bannen) to the remote Cornish island of Balfe to see the effects of a recent oil spill from a shipwrecked tanker. As Shaw sails over on the boat there, the ferry captain (George Woodbridge) lets him know that the islanders keep themselves very much to themselves, but Shaw informs him he isn't planning to stay long anyway and he would like to be picked up tomorrrow afternoon. However, he doesn't count on a true mystery on Balfe - what are the locals hiding?
If that opening sounds a bit like The Wicker Man, then at least the Doomwatch movie could say it got there first with this plot. In fact, after a first half hour or so that sticks surprisingly close to the better known horror's similar first act, it settles into an investigation more fitting for the television series that inspired it. Unlike a British sitcom movie, this effort doesn't concentrate on the cast of the original as they play a supporting role here, with newcomers Bannen (in the sort of Robert Powell role, Powell having made his name in the series before being spectaculalry written out) and Judy Geeson as a schoolteacher on the island helping him.
But she has to be persuaded first, as everyone on Balfe is taciturn at best, hostile at worst. Shaw has an advantage with Geeson's Victoria Brown in that she just arrived on the place a couple of years before and so has a comparable status, only she sides with the community by wishing to keep their secret. We're well aware there's something up when the prologue features a small child being buried in the woods, and later on we catch sight of locals who have an odd appearance around the face, only in fleeting shots, but enough to set alarm bells ringing.
The sense of an insular society unfriendly to outsiders is well handled, and scritpwriter Clive Exton evidently suffered a bad rural holiday at some point because he writes as if he knows of what he speaks. It's not that the film goes downhill after we - and Shaw - find out what is really going on, it simply changes tack and becomes something more faithful to the source. This means an in two minds approach to authority, as while we have to put great trust in the Doomwatch department to sort out the scandal, we also have to mistrust the other scientists and bunglers high up who instigated the problems in the first place.
To add tension, whatever is afflicting the islanders is making them aggressive as well, which may mean the odd fight in the pub and even a chap jumping out of a window, but is too clearly an attempt to include an element of peril to Shaw's presence there. George Sanders essayed his final role here, as a Navy Admiral who may be privy to the information of what is behind the pollution (but maybe isn't after all) but the main conflict here is not really authority-based and more between the public and the mistakes of science, which puts Shaw in a difficult position. He strives to be reasonable to save the community, but has their ignorance and fear to contend with, and no wonder when he represents to them the personification of the outsiders' threat to their way of life. Doomwatch never quite gets exciting enough, or fulfils its early promise, but its thoughtful quality holds the attention nonetheless.