Set in Naples at the end of the 19th century, I Guappi tells the story of a strange friendship between the powerful and charismatic Camorra boss, Don Gaetano (Fabio Testi), and one of the many scugnizzi who grew up on the streets, Nicola Bellizzi (Franco Nero). Nicola, thanks to Don Gaetano's protection, becomes first an honoured picciotto of the Camorra and then a lawyer. He tries to break away from his 'family', but falls back into a life of crime and violence.

Efisio Mulas is a meek laborer who lives with occasional work, especially in Don Leandro Sanna's salon, and rounds up the slim balance by betting with colleagues in strength with the game "head against head". In the village the Sanna and Porcu families' conflict has lasted over a century.

A journalist could marry the daughter of a tycoon, but prefers a relationship with a married woman. An attorney renounces her lover by greed. A soldier tries to approach a widow on a train. A German couple looking for adventure mistakingly aim for the wrong target, yet find love.