Greece's Ionian Islands face the intrusion of the Italian Army, which establishes a sizable garrison along with some German forces on the serene island of Cephalonia. The local populace capitulates immediately. Among the occupiers is Captain Antonio Corelli, an officer from the Italian 33rd Acqui Infantry Division, known for his cheerful demeanor and passion for the mandolin. He takes it upon himself to instruct his soldiers, who have yet to fire a shot in battle, in the art of choral singing. Initially, his presence disturbs many villagers, particularly Pelagia, the strong-willed and educated daughter of the village doctor.
At first, Pelagia is put off by Antonio's antics, but gradually, she begins to appreciate his charm and musical talent, especially as circumstances force them to share her father's home after he offers sanctuary to the captain in exchange for medical supplies. As Mandras, Pelagia's fiancé and a local fisherman, departs for the mainland to fight, the bond between Antonio and Pelagia deepens. His admiration for her beauty and intellect turns into affection, while his experiences with the vibrant local community lead him to question the reasons for his involvement in the conflict.
As the war looms closer, the joyful moments shared between Antonio and Pelagia become increasingly precarious. The Italian government's surrender to the Allies sets the stage for chaos, as German forces insist on disarming their erstwhile Italian allies with brutal consequences. The Greek villagers, facing the wrath of the incoming German troops, try to coordinate a brief yet hopeless resistance, which results in the slaughter of thousands of Italian soldiers branded as traitors by the German High Command.
Among the surviving soldiers is Corelli, who is protected by one of his men, who sacrifices himself to save him. Eventually, Mandras discovers Antonio still alive among the dead and escorts him to Pelagia and her father for healing and recovery. However, tensions rise when Mandras reveals that he saved Corelli not out of camaraderie, but in a desperate hope to rekindle his love with Pelagia. Despite their tumultuous feelings, the couple’s relationship remains strained, and they part ways.
Years later, in 1947, Pelagia receives a surprising parcel from Italy, containing a record of the tune that Corelli had composed for her, yet no accompanying note. An earthquake shakes the village, destroying much of the infrastructure, including the doctor's residence. Yet, life on the island persists, and it seems fate has not yet finished with Corelli and Pelagia, as he eventually returns to her once more.
