In turn-of-the-century San Francisco along the Barbary Coast, crime is running rampant. At the Golden Gate Casino, towering bouncer Moose Moran is outside when his boss, Cash Conover, arrives. When a guest complains that he's lost all of his money and threatens to kill himself, Moose restrains the man. However, Cash tells Moore to let the man go and then gives the destitute gambler a few dollars and wishes him luck.
Elsewhere, the head of the local KKK, Robin Templar, tells his white-hooded followers that they will march on the criminals of the Barbary Coast, and the righteous will soon join them.
On the docks, a one-eyed sailor named Joe hook finds a corpse and searches the man. He finds a KKK robe tucked beneath the man's jacket, and a piece of paper that he pockets.
Templar preaches to his "Crusaders" that they must serve as the law because the authorities are all corrupt. He promises to raise enough money to punish everyone who deserves their fate.
Lt. Tully and his partner Hatch are walking along the docks and spot Joe. Joe insists that he had nothing to do with the corpse turning up dead, and tells Tully to get permission from Chief of Police Keogh to hand him. The sailor points out that Keogh will first have to get permission from Cash, and Tully warns Hatch that Joe must work for Cash. Despite that, he tries to stop Joe from leaving. Joe shoves Hatch in the water and runs out while Tully helps his partner.
Bret Hollister takes his fiancée Clio Du Bois by carriage to the area. When she reminds her future husband that his father didn't pick them up when their boat arrived from Paris, Bret insists that his father was busy with a cattle drive. He tries to direct Clio to more genteel surroundings, but Clio insists on going to the Golden Gate Casino.
At the Golden Gate, Cash hugs one of his croupiers, Flame. One professional gambler, Diamond Jack Bassiter, insinuates that Cash's tables are rigged and Cash tells Jack to go back to his own casino. Undeterred, Jack flirts with Flame and offers to buy her from Cash, but Flame tells him not to mouth off. Jack hesitates and then puts down another bet.
Bret brings Clio inside and the customers insult him for his fancy clothes. When one insults Clio, Bret slaps him and goes for his gun, and the heckler quickly apologizes. At the roulette table, Cash offers the couple his congratulations and Clio wonders if she's met Cash before. He says that he hasn't and advises Bret to watch his step. Once he leaves, Bret tells Clio that Cash won the casino in a poker game two years ago, and Clio suspects that she met Cash in New Orleans.
After the rally, Templar reminds his lieutenant that they can make big money by stealing from the corrupt. He plans to find a man to make an example of, someone who won't be missed and has recently committed a capital crime. Templar figures that they can find such a man at the Golden Gate.
Joe approaches Moose and confirms that Cash is inside, and then runs in as Tully and more officers give pursuit. Once inside, Joe starts a fight as a distraction while Moose tries to stall the policemen. They soon shove past the bouncer and spot Joe running up the stairs. After firing a few shots in the air to quiet everyone, Tully and Hatch go up the stairs. Cash stops them and offers his hospitality, but Tully demands to see Joe. Cash tells him that Joe isn't upstairs and invites the policeman to search the place.
Tully and Hatch enter Cash's expensive office and find an open window, and figure that Joe has escaped. As the officers leave, Templar and his men come in. Meanwhile, Clio keeps glancing over at Cash, and Flame advises her to stick to winning at the table. As the two women trade barbs, Jack places a bet and Bret tries to ignore him.
In his office, Cash goes through a secret passage in the fireplace down to a well-appointed underground chamber. "Joe" is smoking a cigar and assures Cash that the governor will pay for the damages Tully and his men caused. "Joe"--actually Jeff Cable--removes his disguise and says that Joe now has to disappear, and assures Cash that it's all in a good cause. When Cash half-heartedly objects, Jeff reminds him that two years ago in New Orleans, Cash killed Governor Despard's son in a duel after the man cheated at cards. Cash had no choice but to go on the run... but Jeff recognized him and threatened to deport him unless Cash provides him with a safe house. He assures Cash that the governor of California also knows Cash's true identity and would be glad to act on it if Jeff "disappeared" under mysterious circumstances.
Cash asks about the dead man Tully mentioned and Jeff explains that the man worked for him, and was coming to tell Jeff about a new secret organization in San Francisco. He shows Cash the KKK robe he found and explains that someone accidentally killed his men when they tried to capture him for interrogation. Jeff then brings out the piece of paper and explains that it has the Crusaders' secret vows, and tells Cash that they have a new assignment.
At the roulette table, both Clio and Jack win big. When Jack suggests that they buy champagne to celebrate, Clio hastily refuses, claiming that the casino doesn't have any peaches to go with it.
Cash reads the paper, with the vows to kill anyone who breaks their vows of secrecy and expose the KKK. Jeff explains that he broke up the KKK several years ago after the Civil War, but he didn't get all of them and the remainder went underground.
Jack and Clio both keep winning, and Jack continues flirting with Clio despite Bret's warnings. The gambler claims that he's just joking. Templar, watching, wonders why Jack doesn't respond and his man Gibbon figures that Jack is afraid of Bret's father. Satisfied that they've found the right man, Templar studies Jack carefully.
Jeff disguises himself as a Chinese coolie and tells Cash that he has a job at the Princess Sontoya Club.
Templar approaches the table and tries to provoke Bret into attacking Jack.
Once he's done with his disguise, Jeff leaves through a secret elevator.
Clio starts losing and Bret tells his fiancée that it's time to go. When Jack offers to stake her, Templar asks if Bret is going to let the gambler continue to insult him. Bret reaches for his gun and Jack refuses to put up a fight when Bret tells him to make the first move. Templar tries to taunt him into drawing, saying that he's yellow, but Jack refuses to rise to the bait. However, once Bret turns his back, Jack shoots him down.
Cash runs out when he hears the gunshot, but one of Jack's thugs is waiting and disarms him. Jack's bodyguard draws on Templar and his men, and the gambler says that everyone will testify on his behalf that Bret drew but then lost his nerve and tried to run. Tully arrives with his squad and Jack surrender to them, cheerfully inviting everyone to come to his casinos. Once he's escorted out, Templar offers to take Clio home. Well aware of the part he played, Clio slaps him and Cash has Flame take her up to his office. He then tells Moose to send word to Brent that his son is dead.
In Cash's office, Cash offers Clio a drink. He admits that he's a criminal because he has to survive on the Barbary Coast, and he once hoped to leave by boat. However, Cash hit a winning streak and won the Golden Gate, and so far his luck has held. Brent comes in and blames Clio for Bret's death, and says that he knows about her family background from his private detectives. Her family lost their fortune and were run out of New Orleans, and Clio went after Bret for his money. Brent storms out and Templar approaches him on the stairs, claiming that Bret was a friend. While Flame watches, the Klansman warns the cattleman that Jack will go free because of his connections and suggests that Brent buy some justice... for the right place.
Cash takes Clio back to her hotel and they find her maid Marie waiting for them. Marie tells Clio that Brent has had them locked out of their room, and Clio admits that she doesn't have the cash to pay for the room. Cash talks privately to the manager, Mr. Speece, and threatens him into giving Clio the Presidential Suite for the weekend. The casino owner insists on paying and then escorts Clio up to her room, claiming the whole thing was a clerical error.
In his jail cell, Jack has a first-class meal brought in. However, drums sound outside and Jack strolls out through the open cell door to discover the hooded Templar and his men outside.
In her suite, Clio tries to give Marie enough money to return to New Orleans. Marie tries to refuse, but Clio wants her to contact her friend Antoine, who works at the governor's manor. She tells Marie to tell them that she has found the riverboat gambler who killed the governor's son.
Tully refuses to hand over Jack and the hooded Templar gives him three minutes to hand Jack over. He points out that if Tully fires on the crowd then he'll be killing decent men.
Clio tells Marie to have Governor Despard send a man with the $25,000 reward for the killer's head. Once he arrives and places a coded message in the newspaper, Clio will collect the money and reveal the killer's identity. Marie questions the plan and Clio says that she's sympathetic toward Brent and Despard, but despises the men who killed their sons.
Jack begs Tully to help him and hides in his cell. The KKK storm the jail and overwhelm Tully and Hatch, then drag Jack out.
A little while later, Cash goes to the Princess Sontoya Club and whispers to Jeff that the KKK hung Jack from a flagpole.
The next morning, Cash and Flame eat breakfast and read newspaper articles about the new vigilantism on the Barbary Coast.
At his law office, Templar reads the same articles and is satisfied that most of the newspaper support his supposed vigilantism. He then gives his men a list to be distributed with the names of 20 other criminals to be sentenced on his orders.
Clio goes to the casino and asks for a job as a dealer. Cash leaves it up to Flame, and Flame has the French woman play one hand of cards for the job. Moose and the pianist, Thumbs, come in and watch the two women play poker. Clio wins with four aces and admits that she cheated, and they figure she's good enough to work as a dealer.
Still disguised as a coolie, Jeff goes to Templar's law office. He overhears Templar ordering his men to hand out the flyers, and then says that he came to the wrong address and leaves.
That night, Cash is watching Clio deal when Moose brings him a death list that was posted on the door. Crime lord Florrie Roscoe comes in with his men and tells Cash that they have to talk because both of their names are on the list. He wants everyone on the list to meet at the courthouse with Keogh the next day, and band together to fight the Crusaders. Cash doesn't trust the crooked police chief, but Florrie tells him to be there and leaves.
A gaslight flickers and Cash goes to his office. Jeff emerges disguised as a bank examiner from Wichita, and says that Brent withdrew $20,000 and paid off the Crusaders. The undercover agent figures that Brent paid to have his son's killer hung, and tells Cash that Robin Templar is the alias of Damon Taylor, a cavalry captain in the Civil War. When Templar's superior, the founder of the KKK, tried to disband the organization because it was too extreme, Templar and a group of renegades rode off. Grant sent Jeff and his fellow agents to stop them, but Templar escaped.
Florrie and his men meet at Florrie's bar. The crime lord figures that by the time the Crusaders get to him, he'll have left San Francisco. One of Florrie's men points out that the Crusaders might not proceed alphabetically. Templar comes in and claims that the Crusaders have retained him as legal counsel. In return for Florrie "donating" $20,000, he'll be spared. Templar advises Florrie to pass the offer on to the others on the list, and points out that no one will believe the crime lord if he claims the Crusaders can be bought off. The lawyer knows all about Keogh and warns Florrie that he'll be on the next list, and tells Florrie to deliver the money before sunset the next day.
The next day, Cash and the crime lords meet at the courthouse with Keogh. The police chief refuses to give in to vigilantes and figures that once they find and arrest Templar then the Crusaders will retreat into the shadows.
That night, policemen are guarding Florrie at his bar. However, the Crusaders burst in and kill Florrie.
Cash goes to the hotel to pick up Clio, and says that it may finally be time for him to leave San Francisco. On the way to the casino, they arrive at the spot where the Crusaders are stringing up Florrie. The vigilantes recognize Cash and knock the driver off of his perch, and Templar tells one of his men to take Cash to their hideout. The man drives the carriage off... but then pulls into an alleyway and lead Cash and Clio into the sewers. Moose and Tully are waiting, and Jeff reveals that he's the Crusader in disguise.
Cash and Clio continue to the Golden Gate and Clio realizes that Flame is jealous. Clio talks to her privately and Flame suggests that they cut for high card to see who stays. The French woman refuses, saying that she can't leave before she stops something that she put in motion.
Cash and Jeff take Tully to Jeff's hidden apartment and explain that he works for the governor. Tully wonders if Templar doesn't have the right idea eliminating criminals, but Jeff insists that killing a man without a trial is still a crime no matter how many innocent men Templar suckers in. Cash figures that they can buy Templar off, and then reveal the fact that the lawyer betrayed their principles for money to the Crusaders. The Crusaders will then abandon him and be powerless without his leadership.
The next day, Keogh meets with the surviving crime lords and admits that he can't protect them all. They agree to pay off Keogh to entrap him and each of them kicks in $20,000 each. Jeff, disguised as an elderly lawyer, goes to Templar's office and says that he can pay him the $380,000 if he'll spare the crime lords. Templar says that he'll consider it and wants Cash to bring the money in person. Jeff agrees and Templar says that he'll have two of his men pick Cash up with the money. The agent says that the crime lords will want a witness along and then gives Templar half a dollar bill so that the man picking up Cash can identify himself with the other half.
Later at the courthouse, Keogh collects the money in a satchel. Jeff poses as the witness--a priest--and a driver brings in the half bill. Jeff and Cash leave, unaware that Keogh has switched the satchel for an empty one.
The Crusaders blindfold Jeff and Cash and take them out of town. Templar and his lieutenants are waiting and lead Cash and Jeff to a hanging tree. The lawyer boasts that he and his personal cadre will disappear with the money, and realizes that Jeff is the same man that broke the Clan after the War. Jeff tosses the key to Templar and then jumps him when he's distracted. Cash and the agent take on the Crusaders and then ride off, leaving the satchel behind. Templar tells his men not to bother pursuing because they have what they need. However, when he opens the satchel, it explodes. Jeff and Cash see the explosion and realize that Keogh made the switch at the courthouse... and has the $380,000 for himself.
That night, Keogh slips into the sewers but Cash, Jeff, and Tully have followed him. They confront the police chief, who admits that he was going to let everyone believe that Templar had escaped with the money so he'd be free and clear. Jeff recovers the money from the sewer drain, and then orders Keogh to resign so Tully can take over. Keogh draws a derringer and takes the money, but backs into the manhole and falls into the water below. Jeff confirms that it leads to a local shanghai bar, and they figure Keogh will soon reap his just rewards.
Despard's man, Jacques Fouchet, summons Clio to his hotel room and demands to see the killer. Clio takes him to the city morgue and shows him what's left of Templar's body. Fouchet points out that there will be no payment without a proper identification, and there's not enough of the body left to do so. However, he offers Clio half of the reward money if he backs her story while he pockets the other half. Clio agrees... exactly as planned.
Later at the casino, Flame tells Cash that Clio is heading back to Paris now that she can afford a ticket. As they leave to celebrate, Jeff--posing as a blind man--winks to Cash and wishes him well.