But their noble goals to help the local peasants are undermined by an increasing sense of isolation and mania.
The legendary Deborah Kerr (From Here To Eternity) heads the cast as the tormented Sister Clodagh, and delivers a dazzling lead performance.
But the film really belongs to Kathleen Byron, who plays the unstable and jealous Sister Ruth with a maniacal physicality and a penetrating stare.
The ever-increasing tension is unnerving in the most thrilling possible way, and elevates what by modern standards is a somewhat middling story to operatic levels.
The film is worth seeing for the costumes alone - the nuns all in white with their rigid headdresses look like ethereal stormtroopers.
But the most amazing thing about Black Narcissus is that despite the pervasive presence of vertiginous cliffs and awe-inspiring distant mountain peaks, the backgrounds were ALL painted.
Co-directors Powell and Pressburger wanted colour to play a large role in the storytelling (like in their other famous collaboration, 1948's The Red Shoes), and thus sought complete control over the look of the film, filming all the mountaintop scenes on a set with backdrops painted on glass.
The brush strokes may be occasionally be visible, but the backgrounds pop visually in a way their modern digital equivalents rarely do. Plus the colour schematics enhance the drama to no end.
Black Narcissus must be seen on a big screen to truly appreciate what Powell and Pressburger were trying to achieve, so check it out at one of the screenings listed in the schedule here.
The Retro Showcase features numerous other classic films that would be a treat to see on the big screen, everything from Gone With The Wind to West Side Story to Labyrinth.
I shall continue to highlight some of my picks here as the season progresses.
Watch the trailer for Black Narcissus: