The film shows how Italy's historic national hero Giuseppe Garibaldi (embodied by Renzo Ricci) leads a military campaign known as Expedition of the Thousand in 1860 and conquers Sicily and Naples. When the Bourbon monarchy has left Southern Italy, he supports Victor Emmanuel II of Italy who achieves a lasting unification under the aegis the House of Savoy. Roberto Rossellini has said he was prouder of this film than of any other film he ever made.

Paola (Lucia Bose) is the beautiful and jealously-guarded younger wife of a shady factory owner, Enrico Fontana (Massimo Girotti). In order to investigate her romantic history he hires a private detective, which ironically brings Paola back into contact with former lover Guido, with whom she resurrects a lost passion. Dogged by the suspicions of their respective mates, they are drawn closer to each other in the face of adversity, and begin to plot Enrico's demise. But when the challenge of being together falls away, will the passion start to wane? A masterpiece of intensity and finely-wrought emotion.