The film covers the time that a small group of nuns occupy an old house at the top of a chasm in the "east" (I'd guess Tibet). The new convent is to be called "St Faith". The rarified air and stupendous views cause crises for many of the nuns (you knew it would, really) and the film covers their conflicts, internal and external.
Powell & Pressburger have made every image a photograph worth printing - they won an oscar for best Cinematography. The view from the convent is as stunning for us viewers as it for Sister Clodagh (et al). The crises aren't stock ones - they vary from madness (chillingly portrayed) to the gardening nun planting flowers, instead of vegetables.
My favourite scene would be the flashbacks of Sister Clodagh, reliving her life with her fiancé prior to the order. One scene has her calling out his name as she leaves the house and stepping into absolute blackness...
Come back, Powell & Pressburger! We need you