'In my head, she's very much this person who has felt really alienated her entire life and has always found it really difficult to connect with other people,' explains British director Rose Glass about the titular character in her fascinating debut feature film.

Saint Maud is a psychological horror about a young nurse who thinks it is her calling to save the soul of a patient in palliative care before she passes away. Morfydd Clark turns in a phenomenal performance as Maud whose loneliness and isolation have led her to religion and on a downward spiral of obsessive behaviour. Jennifer Ehle plays the patient, an exuberant ex-dancer called Amanda whose lifestyle and love life aggravates Maud.

Set in an unnamed British seaside town and filmed in Scarborough, Maud hauntingly glides between sandy beaches, her tiny accommodation and the grand home of her patient. 'I grew up in Essex and there's a lot of interesting seaside towns round there,' explains Glass. 'There's something that's slightly not real about those places. Anywhere that's got arcades and all that kind of kitsch funfair stuff feels a bit surreal. The film is set in the present day and in the real world, but I wanted it to be a slightly celestial version of it. Scarborough seemed to do that nicely. Geographically, it's surrounded by nothingness, the ocean on one side and then the hills on the other isolate it and makes it feel like they're in a little bubble.'

Glass cites Iain Banks' The Wasp Factory and Fyodor Dostoevsky Notes from the Underground as touchstones for the way she wanted to present Maud's inner life. 'I told both Morfydd and Ben [Fordesman], our cinematographer to read Notes from the Underground. I thought it may be useful to get that interior monologue from the book to get inside this neurotic anti-hero, who swings between tremendous arrogance and self-loathing. It's a very funny book as well … I think a lot of people didn't quite believe me when I said there was going to be jokes in Saint Maud.'

A visually arresting, confrontational and visceral experience, Glass places the viewer inside Maud's head. For inspiration on that, she looked to the early work of Roman Polanski, like Repulsion and Ingmar Bergman's Persona. 'I knew the film had to exist in its own private universe with shadowy and seductive characters emerging out of the darkness. There's something very heightened and sensual about the whole thing. The entire film had to feel incredibly subjective and we had to feel Maud's perspective on the whole thing.'

Glass concludes, saying 'On the one hand, what happens in the film on a literal level is quite a small, sad story about a traumatised nurse not really getting the helps she needs, but the story I wanted to tell was much more about what she thinks she's going through. The journey she's going through is biblical and grandiose – she's on a mission from God. She's having spiritual revelations on a regular basis, both good and terrible. The style and aesthetic of it all had to be as intense as what she's going through.'

Saint Maud screens at Glasgow Film Festival, GFT, on Sat 7 Mar as part of the FrightFest strand. General release from Fri 1 May.