ast year, Morfydd Clark appeared in Armando Iannucci’s new version of David Copperfield playing both David’s mother and the woman he’s in love with – a Freudian-doppelganger performance so coolly understated that many didn’t realise it was happening, or quite why they found Clark’s appearance(s) so disquieting. Well, there’s nothing understated about her now, and what a sensational breakthrough in this extraordinary horror melodrama from first-time feature director Rose Glass. Clark gives an operatically freaky turn that knifed me in the kidneys, the way Catherine Deneuve did in Repulsion or Emily Watson in Breaking the Waves. And her final split second on screen is the equivalent of brutally pulling out the knife to start the internal bleeding. It’s a scary movie that is also a satirical nightmare about the physical and erotic intimacy of nursing. The setting is the seaside town of Scarborough, along whose seafront and garish arcade frontages Maud is in the habit of going for moody solo walks. She is an intense and lonely young woman living in a scuzzy bedsit, employed as a private agency nurse and palliative caregiver. She prays often, asking to be delivered from incessant stomach pains. It seems at first that Maud is a cradle Catholic, and these are the moral certainties that she has imbibed since childhood. Could it be that she has been named after Saint Maud, the 10th-century Saxon queen renowned for piety and caring for the sick? She carries round her neck an image of Mary Magdalene, which she has “ordered online”. But it is only when Maud bumps into an old nursing colleague, Joy (Lily Knight), that we realise that her persona is not exactly what it seems. Maud is yearning for some moment of revelation or exaltation, some great reckoning or trial that will make sense of her life and faith. And this seems to have arrived when she is assigned to look after Amanda Köhl, terrifically played by Jennifer Ehle, a once brilliant dancer and choreographer who now has a neurological disease that means she uses a wheelchair. Amanda is now angry, cynical and cantankerous. (In a heartwarming comedy of course, Maud and Amanda would, after a rocky start, become best pals, learning life lessons from each other’s vulnerabilities. Not in this film they don’t.) Amanda has become what an exasperated friend calls a “Norma Desmond” figure, and this hardly bodes well for the relationship with the prissy, prudish Maud when Amanda’s other caregiver comes by – Carol (Lily Frazer), whom Amanda pays for sex. But, strangely, Amanda is amused and touched by Maud’s own transparent pain and frowning childlike concern for her patient’s soul. She consents happily to being bathed by Maud (without her hairpiece) and even starts asking her about her religious beliefs and does this with detachment but not mockery, and even sympathy. And the tragi-ironic point is that Maud is a good nurse (for a while). She is utterly devoted, and her physical therapy sessions with Amanda, massaging and manipulating her legs and torso, are good for them both. Clark’s performance shows how there is something in these experiences that speaks to a need that has been thwarted or denied or displaced in Maud. But a terrifying flashback conflating a sexual experience with psychotic violence and a CPR episode gone horribly wrong shows how the physical touch of nursing now means something different for her. Yet Amanda listens kindly to Maud’s shy explanations about how and when she feels God near her, and perhaps to humour Maud (or even maybe not) declares that she possibly feels the presence, too. A kind of spiritual love affair or redemption drama begins to develop in poor Maud’s head. But Amanda’s actual views and actual needs are such that this can only end one way. The outbreaks of pure horror are arguably familiar; staring at cockroaches on the ceiling is something that I seem to have seen before, and Glass obviously intends an allusion to The Exorcist at one stage. But the film punches out its warped drama with amazing gusto and Clark is lethally assured: not Saint Maud really, but Saint Joan, a spectacular horror heroine. • Saint Maud is in cinemas.