Maria is engaged to Carlo, a handsome young man of large means, being the son of a well-known Naples merchant who owns a bar; Maria's brother, Paolo who emigrated to Argentina, is romantically linked to a very attractive young woman, Lucia, the daughter of an unscrupulous woman who manipulates her at will.

Distraught Maria returns home and meets her doorkeeper who, having also lost a daughter seduced and abandoned by an unscrupulous man, decides to avenge Mary on her.

Meanwhile, Paolo has arrived and after reading the letter he meets Carlo at his home while he reconciles with his sister.

Paolo forces Carlo to reveal the meeting place and rushing to the hotel he finds Lucia and kills her blinded by her jealousy.

The last shot shows the red moon which, as he himself said when getting off the ship, is a harbinger of bad luck and tragedy.