An outsider visits a remote isolated village that has seemingly shunned modern life. Dr. Del Shaw, an investigator from the British ecological watchdog group nicknamed Doomwatch, is sent to the island of Balfe to file a report on the effects of a recent oil tanker spillage. He becomes fascinated with the mysterious behavioural disorders of the locals who display rudeness and random aggression and a strange genetic prevalence of thick lips and sloping brows. Investigation shows that the villagers have been suffering over a prolonged period from hormonal disorders, which are being caused by leaking drums of growth stimulants that have been dumped offshore. The islanders have been eating contaminated fish and develop a disorder of excessive hormonal growth, which produces aggression and eventually madness, attributed to a form of acromegaly. Rather than seek help from the mainland, they hide those who are deformed from any newcomers.

• Ian Bannen as Dr. Del Shaw
• Judy Geeson as Victoria Brown
• John Paul as Dr. Spencer Quist
• Simon Oates as Dr. John Ridge
• Jean Trend as Dr. Fay Chantry
• Joby Blanshard as Colin Bradley
• George Sanders as The Admiral
• Percy Herbert as PC Hartwell
• Shelagh Fraser as Mrs. Betty Straker
• Geoffrey Keen as Sir Henry Leyton
• Joseph O'Conor as Vicar
• Norman Bird as Brewer
• Constance Chapman as Miss Johnson
• Michael Brennan as Tom Straker
• James Cosmo as Bob Gillette

The film was made at Pinewood Studios and location shooting took place around Polkerris, Mevagissey and Polperro and Chapel Porth in Cornwall, as well as the London Heliport in Battersea.^{[citation needed]} The sets were designed by the art director Colin Grimes.

The Monthly Film Bulletin wrote: "Though it might seem appropriate that Peter Sasdy, a former TV director, should turn a successful TV series into a feature film, his version of Doomwaich unfortunately owes more to his work for Hammer than to his early experience. After a promising opening – with a man burying his daughter's body in the woods, and the titles rolling up over newsreel shots of sea birds killed by oil pollution – the weak, science-based story-line is embellished by Gothic horror elements which serve only to vitiate the authenticity that was the chief strength of the otherwise glossy TV series. To inject excitement and suspense into the film, Sasdy relies on Hammer film clichés (Del's early encounter with the hostile villagers in the pub might have been transplanted direct from Transylvania and Elstree) and on the over-acting of various island notables (especially Shelagh Fraser's village storekeeper). Nor is the film helped by the importation of two stars and the relegation of the original Doomwatch team to minor roles. The Gothic exaggerations and the scientific revelations never really cohere, and for all the topicality of the plot, Sasdy's film proves equally unconvincing as ecological exposé or contemporary horror show."^[2]

For Radio Times, Tom Hutchinson awarded the film two stars out of five, writing "this mystery thriller crash-landed unhappily in the swamp of horror instead of on the firmer ground of science fact or fiction [...] It's risibly alarmist, certainly, but the environmental dangers it pinpoints are only too topical."^[3]

Halliwell's Film Guide described it as "an unsatisfactory horror film".^[4]

• Doomwatch at IMDb  
• Doomwatch then-and-now location photographs at ReelStreets