In the mid-nineteenth century, Spider Burke's men make a mistake when they try to shanghai sailor Bat Morgan.  Bat overcomes his attacker and sends him off to sea in his place.  With his earnings, Bat heads to Paul Morra's saloon on the Barbary Coast.  There, he confronts the Shanghai Duck, a man who earns his living by selling men as sailors to ships heading for China.  During their fight, Bat kills the Duck.  Crusading newspaper editor Charles Ford, who witnesses the struggle, congratulates Bat for winning an unfair fight and for killing a worthless man.

Impressed, Morra offers Bat a job.  Under the sponsorship of politician James Daley, ambitious Bat organizes the Coast against Ford, who is fighting to clean up vice conditions there.  Using the money he makes from the arrangement, Bat opens up his own saloon, which is elegant enough to attract society people.

Tired of Ford's campaign against the Coast, Daley plans to kill him.  When she learns of the plan, Jean Barrat, the owner of the paper, begs Bat to prevent the murder.  Out of respect for Ford and love for Jean, he does.  Although Jean returns Bat's love, she feels that they are separated by their different attitudes toward the Barbary Coast.

In an effort to lure society people away from the Coast, Judge Crawford brings an opera company to town.  Bat passes out tickets to everyone who works on the Coast.  At the opera, Crawford insults Morra, who responds by killing him.  Ford then declares war on the Coast and Daley kills him.  Outraged by the murders, Jean runs an editorial calling for the organization of vigilantes.  The vigilantes hang Morra and Daley and then move on to the Coast, burning down buildings as they go.  The mob arrests Bat, intending to hang him until Jean passionately pleads for his life.  Moved by her argument, the crowd agrees to parole Bat into Jean's custody, and at last Bat and Jean are on the same side.