The story is taken from the drama "I Pescatori" (The Fishermen) by Raffaele Viviani, and is set in a fishing island off the coast of Naples (clearly identifiable with Ischia). Here lives Concetta, a widow with two children, who now lives with another man who however secretly lusts after his stepdaughter until when, on a stormy night...
Streaming availability for US region, via JustWatch.
