4, is an opera in four acts, composed by Riccardo Zandonai, with a libretto by Tito Ricordi II [it], after D'Annunzio's play Francesca da Rimini.

But as Francesca would certainly refuse to marry the lame and deformed Gianciotto, she is introduced in the first act, by means of a well-laid plot, to his handsome younger brother, Paolo, known as Il bello.

They then dance and sing in celebration of the advent of Spring, until, on a whispered word from her slave, Francesca dismisses them.

He enters; they continue reading the story of Guinevere together, until, no longer in control of their feelings, they let their lips meet in a long kiss.

In the fourth act, Malatestino, Gianciotto's youngest brother, who himself lusts for Francesca, has discovered her secret meetings with Paolo.