Roy Boulting’s Twisted Nerve is an unsettling psychological thriller that leans heavily on a sensationalised – and deeply flawed – portrayal of mental illness. The film follows Martin Durnley (Hywel Bennett), a troubled young man who assumes a childlike alter ego, “Georgie,” as a coping mechanism. After a failed shoplifting attempt, he latches onto a kind-hearted student, Susan Harper (Hayley Mills), spiraling into obsession with deadly consequences.

Despite its eerie atmosphere and chilling central performance by Bennett, the film is tainted by its pseudo-scientific premise. The idea that a hereditary “twisted nerve” could predestine mental instability, particularly through a link to Down’s syndrome, is not only outdated but also ethically dubious. The film’s opening narration posits this as a scientific truth, using it as a MacGuffin to justify Martin’s homicidal tendencies, a choice that has understandably drawn criticism over the years.

Director Roy Boulting, best known for his satirical British comedies, takes an unexpected turn into thriller territory here, crafting moments of genuine suspense. His direction ensures a polished visual style, aided by Bernard Herrmann’s menacing score—perhaps the film’s strongest asset. However, Boulting’s handling of the subject matter is clumsy, leaning into shock value rather than genuine psychological depth.

Hywel Bennett delivers a convincingly unnerving performance, switching between the vacant innocence of Georgie and the calculating menace of Martin. Hayley Mills, fresh from her Disney stardom, takes on a more mature role as Susan, though the script limits her agency, reducing her to the archetypal oblivious victim. Billie Whitelaw and Frank Finlay add solid support, but ultimately, the film struggles to balance its thriller elements with its problematic premise.

While Twisted Nerve succeeds in unsettling its audience, it leaves a sour taste with its outdated and irresponsible approach to mental illness. As a psychological thriller, it has its moments, but its reliance on dubious genetics as a horror device ultimately weakens its impact.

• Saul Muerte