The story unfolds around Stiffelio, an Italian Protestant priest, married to Lina. The opera caused a furor during its time as the setting is contemporary to the clergy-hating Verdi and the fact that Lina is having an affair with another man. The greater scandal was that Stiffelio, during his final sermon, still not knowing how to act, opens the Bible on the page where he reads to himself: "He who is fully without sin shall cast the first stone...."

He thus decides to forgive her, in front of the massed church. This was, of course, unacceptable to the moral majority of Catholic Italy during that time. 

This opera was revised by Verdi in 1857, into a new four act opera Aroldo.

The original Stiffelio disappeared from the repertory and won its first modern revival only in the 1960s.  Since then it has received a fair number of performances, including a notable production at Covent Garden in 1995, starring José Cura.