César runs a bar along Marseilles' port, assisted by his 23 year old son, Marius. Colorful characters abound: M. Panisse, an aging widower and prosperous sail maker; Honorine, a fishmonger with a sidewalk stall near the bar; her daughter, Fanny, who helps her sell cockles just outside the bar; and various old salts. Friends since childhood, Fanny and Marius love each other, but Marius has a secret wanderlust: every ship's whistle stirs a longing for foreign lands. When M. Panisse seeks Fanny's hand in marriage and when a departing clipper needs a deckhand, Marius and Fanny must decide who and what they love most. César, with his generous, wise spirit, tries to guide his son.

Picking up moments after the end of Marius, this film follows Fanny’s grief after Marius’s departure—and her realization that she’s pregnant. Panisse continues courting her and embraces the baby’s impending arrival as a gift, so long as its paternity remains a secret. Fanny and Panisse wed, but after her baby’s birth, Marius returns unexpectedly and demands what he believes is still his.

Honoré Panisse is dying, cheerfully, with friends, wife, and son at his side. He confesses to the priest in front of his friends; he insists that the doctor be truthful. But, he cannot bring himself to tell his son Césariot that his real father is Marius, the absent son of César, Césariot's godfather. Panisse leaves that to Fanny, the lad's mother. Dissembling that he's off to see a friend, Césariot then seeks Marius, now a mechanic in Toulon. Posing as a journalist, Césariot spends time with Marius and leaves believing tales he is a petty thief. Only after the truth comes out can Marius, Fanny, César, and Césariot step beyond the falsehoods, benign though they may be.