On the New Orleans shipping docks, an open hiring call for workers dissolves into a free-for-all fistfight led by representatives of racketeer Zero Saxon, who intends to stifle outside competition for the men. When ex-naval officer Dan Corbett arrives at the docks looking for work, he is put off by the brawl, and goes instead to a shipyard, where he negotiates the purchase of a surplus LSM craft, with which he plans to use to start his own shipping business. The shipyard owner agrees to allow Dan to make payments, recommending that he might find work at the shipyard by attending the longshoremen picnic. At the picnic, Dan is befriended by Alma Mae, the girl friend of Jack Petty, business agent for the longshoremen's union. When a drunk makes a pass at Alma, Dan knocks him out, impressing Alma, who reveals that the man is the union's top boxer. Later, Dan asks Alma if she can help him get a job and, per her advice, the next morning meets Joe Reilly, Saxon's dock manager. Joe explains that Saxon succeeds by underbidding all the other wharfs in the city, and Dan agrees to sign on. That night, Dan meets Joe and his wife Marie for dinner and is introduced to Scrappy Durant, Marie's brother, a former boxer turned coach, who offers to help Dan box for the union. Over the next several days on the dock, Dan works hard, but is confused when Joe rebukes him for wanting to check the papers on a suspicious shipment. Dan accepts another dinner invitation from Joe and Marie, but when he arrives that night, he and Marie wait in vain for Joe. Unknown to Marie, Joe goes to Saxon to request a release from his job, having saved enough to go into business for himself. Saxon agrees, but after Joe departs, sends his henchmen, Deuce and Big Mike, to kill Joe because of his extensive knowledge of Saxon's operation. Upon the discovery of Joe's murder, New Orleans police and local politicians join with the head of the longshoremen workers to discuss the racketeers' stronghold on the docks. Marie tearfully tells Dan that she expected Joe's death, but Dan remains shocked by the murder. Shortly afterward, an insurance agent arrives at the docks to investigate a report of missing supplies. The dock supervisors interfere with the agent's inspection, causing him to impound a questionable shipment. Late that night, per Saxon's orders, two men dump gasoline near the impounded shipment and set it ablaze. Dan, working late, hastily pushes the burning shipment off the dock with a forklift to prevent the fire from spreading. The next day, Al Chittenden, president of the Longshoremen Association, chastises Petty for allowing the fire to occur. Petty, a close associate of Saxon's, is ordered to build up Dan as a hero to placate Chittenden. Alma asks Dan to her apartment for cocktails to inform him that at the longshoremen's tribute to Joe, Dan will also be honored for his role in the dock fire. At the dinner, Dan is pleased to be publicly acknowledged by Saxon. Scrappy later tells Dan that Marie believes that Dan is being used by Saxon and details how Saxon uses complex paperwork to cover his illegal activities. Soon after, Saxon summons Dan and offers him an enormous salary increase to take Joe's job. When Dan asks frankly how the large salary is possible within union rules, Saxon is evasive, and Dan departs uncommitted. Believing that Scrappy may have counseled Dan, but knowing that another killing would draw too much police scrutiny, Saxon orders Deuce and Big Mike to force a conflict between Dan and Scrappy. At the gym, Deuce tells Scrappy that Dan has confessed that Scrappy advised him of Saxon's operation. Angered, Scrappy attempts to provoke Dan in the ring, and confused, Dan finally lashes out at Scrappy and is mortified when the coach collapses, dead. Later, Marie tells a stunned Dan that he is not to blame, as Scrappy had a bad heart, which only the family and Saxon knew about. When Dan recalls Deuce and Big Mike's presence at the gym, he informs the police and Chittenden of the activities he has witnessed on the docks and Scrappy's disclosures. The police ask Dan to plant a radio monitor on one of the Saxon shipments to track its movements and soon discover the complicated ring of outlets Saxon uses to move around supplies. When Saxon discovers the monitor, he attempts to gain access to incriminating papers housed in one of the dock warehouses. With the police still unable to arrest Saxon, Chittenden assists by ordering the longshoremen to strike, thus impeding any access to the docks by Saxon's men. Saxon sends Big Mike to beat up Dan for his complicity with the authorities, but Dan is revived by Alma, who offers him information about Saxon's involvement in Joe's murder in exchange for immunity. Dan locates Saxon, who has secretly entered the warehouse, and is wounded in a fight with him before Saxon is eventually arrested. Several months later, Dan and Marie relax on board his LSM as they hear the news of Saxon's indictment.