The Bay Of Noon by Shirley Hazzard

The scene is Naples, against whose ancient and fantastic background the modern action takes place. Among the protagonists is Jenny, young and pretty, who has come to Naples in flight from a sombre drama, unaware that a larger drama waits her there. She has an introduction to a Neapolitan woman, and one day she idly follows it up.

This is her leap through the looking glass.