Joe Morse, an attorney for racketeer Ben Tucker, realizes that thousands of people select the number "776" in the lotteries on Independence day and conceives of a clever scheme to fix that as the winning number on the Fourth of July, thus bankrupting the numerous numbers banks operating in the city and enabling Tucker to gain a stranglehold on the racket. Joe is motivated by Tucker's promise to consolidate the new syndicate under his brother Leo's small-time numbers operation. Knowing that Leo, an intrinsically honest man in a dishonest business, will resist joining the syndicate, Joe goes to visit his brother on the eve of the Fourth at his numbers bank, hidden in a small apartment in the slums. Joe offers his brother a piece of the impending combine, but Leo denounces the proposed alliance with Tucker, then excoriates his brother's lack of principles and reminds him of the sacrifices that he has made to put him through law school. To save his brother from financial ruin, Joe arranges for Leo's bank to be raided that night, thus assuring that it will be closed the next day when 776 hits. After Joe leaves, Leo's young secretary, Doris Lowry, who witnessed Leo's barrage, tearfully informs her boss that her conscience will no longer allow her to work for him. Soon after, the police arrive and arrest everyone on the premises, including Doris, Leo and his meek bookkeeper, Freddy Bauer. Although Leo refuses Joe's help, Joe goes to the jailhouse and pays everyone's fines. When Leo announces that tomorrow will be his last day in business, Joe advises him to close immediately, but Leo insists on honoring his patron's bets. Feeling responsible for Doris' arrest, Leo asks Joe to escort her home, and along the way, they discuss issues of ambition and guilt. The next day, July 4th, all the numbers banks in the city are thrown into bankruptcy when the number 776 hits. Joe pays another visit to his brother, and now ruined, Leo reluctantly enters into an alliance with Tucker. Encountering Doris in the lobby of Leo's apartment building, Joe justifies his actions by assuring her that his brother really wanted to be forced into the combine. During the first day of reorganization, Tucker's men take control of Leo's operation, and Bauer, terrified, states his intention to quit, but Joe uses implied threats to convince him to stay on. In desperation, Bauer determines to drive Tucker out of business by informing Link Hall, the city's new special prosecutor, of the location of Leo's bank. Later, as Bauer is leaving the office, he is approached by Wally, an emissary from Tucker's business rival, Ficco, who asks him to arrange a meeting between Ficco and Leo. That evening, Joe finds Tucker's flirtatious wife Edna and Doris waiting to see him at his office. After Edna warns Joe that her husband's phone has been tapped, Joe, sensing the law closing in on him, checks his private line to Tucker. Troubled, Joe leaves the office with Doris and confides his fears and self-doubts to her. Following Bauer's tip, the police raid Leo's bank the next day, arresting Bauer, Leo and Doris once again. When Tucker vows war on Ficco, Joe, sensing trouble, asks Tucker to release Leo from the bank and promises to take his place, thus opening himself up to criminal charges. As they await arraignment, Doris, blaming Joe for her arrest, denounces him and warns that he will be responsible for Leo's death. Afterward, Leo refuses Joe's offer to buy him out and discovers that Bauer was his betrayer. That night, Joe returns to his office and finds an intruder there. After the man leaves, Joe extracts a wad of cash from his safe and flees the building. Leo, meanwhile, fearing for Bauer's safety, gives him a ride in his car. When the frightened Leo wanders off by himself, he is accosted by Wally and forced to set up a meeting with Leo. As soon as the unsuspecting Leo enters a café to meet Bauer, Ficco's men rush in, shoot Bauer and kidnap Leo, who then suffers a heart attack. Joe, meanwhile, has finally come to the realization that he has ruined his life. In a restaurant, as Joe drunkenly tells Doris his plans to run away, Doris fights for his salvation. When Joe spots the morning newspaper headlines trumpeting Leo's kidnapping, he runs out of the restaurant. Just as Ficco and Tucker reach an accord at Tucker's apartment, Joe pounds at the door and Tucker informs him that he has gone into business with Ficco. After Ficco coolly declares that Leo is dead and that his body has been dumped under a bridge, Joe, filled with vengeance, surreptiously picks up the receiver of Tucker's tapped phone. When Joe begins to recite a litany of Tucker's crimes for Hall to hear, Tucker realizes what is happening and attacks Joe, extinguishing the lights in the process. In the darkness, all three men nervously finger their pistols. After stalking Tucker, Joe kills him and then turns his gun on Ficco. Then, picking up the phone receiver, Joe declares that he is on his way to police headquarters. First, however, he goes with Doris to find Leo's body under the bridge. As they walk away, Joe voices his determination to join Hall in his battle to end corruption.
