The Fiend (also known as Beware My Brethren)[1][2] is a 1972 British horror film produced and directed by Robert Hartford-Davis and starring Ann Todd, Tony Beckley and Patrick Magee.

The film opens with shots of a terrified young woman in a mini skirt fleeing for her life along a riverbank, interspersed with scenes of a Brethren baptism service in full swing complete with gospel-style music and the congregation working itself into a religious frenzy.

The girl is finally cornered by her unseen pursuer, strangled, stripped naked and thrown into the river at the same time as a boy is symbolically submerged during the baptism service.

Birdy meanwhile is in failing health; a diabetic, she is dependent on insulin to control her condition but has to obtain supplies surreptitiously as the use of medicine is strictly forbidden by the Brethren's beliefs.

A generally good cast, including Ann Todd and Patrick Magee, do the best they can under the circumstances, but the odds are all against them, especially since most of the film is constructed in a series of ugly, staccato close-ups.

"[3] Brian Orndorf of Blu-ray.com wrote that the film "begins with a blast, but soon settles into a series of tedious encounters and dull supporting characters", and that it "[comes] across as a television movie that's occasionally interrupted by scenes of violence and nudity.