A young seminarian who can't be ordained because of a speech impediment leaves the seminary to take a job with a wealthy baroness' crippled son. The seminarian is actually what the italian title of the movie describes as an exploitative parasite (saprofita), first bedding the baroness and consequently pushing her impotent husband to commit suicide, then taking off to Lourdes with the boy, who hopes for a miracle, and finally seducing a very devout woman who is visiting the site with her grandmother, who unexpectedly dies.
In the city of Ostuni in Puglia, the mute seminarian Ercole is designated to be the driver and nurse of Parsifal, the paraplegic son in a rich and sanctimonious family of landowners. Ercole soon becomes the lover of his master's wife, the beautiful Baroness Clotilde. In a familial and social context where only money, sex and power count, everyone tries to take advantage of everyone, but the real saprophyte turns out to be Ercole.
Cheating scenes are in the first 30 minutes of the film. The wife's full-on sex with the seminarian is at 25:56. That's after they seduce each other while they both bathe her son. The son peeps on them doing it and then masturbates in his bedroom. After the two finish fucking, the wife's husband, apparently aware of their tryst, jumps off a window and kills himself.