Her books usually take place in a closed world, a school or convent or a hostel. But Spark's novels always have a central figure who is in the grip of a delusion, and is in some way trying to play God, whether it be Brodie with her schoolgirls or the Abbess with her nuns. Not that the central character is usually the only person to be deluded: many, or even most of the ancillary characters are always in the grip of some degree of fantasy or misapprehension. Any one of her books could take as its epigraph TS Eliot's line, "humankind cannot bear too much reality" - though we should add the qualification that in Spark's world, it's by no means clear that humankind can bear any reality, ever.
--John Lanchester, "An Act of Faith"