One night in Manhattan, slick, up-and-coming press agent Sidney Falco scans the column of New York Globe writer J. J. Hunsecker, an immensely popular journalist whose column and radio show have great influence in the entertainment world. Because J. J. has, for the fifth day in a row, neglected to publicize any of Sidney’s clients, Sidney’s business is rapidly failing, despite his attempts to placate each client. In consternation, he turns cruelly on his sweet secretary, Sally, but then explains that his drive for success forces him to curry favor with J. J., who is snubbing him for failing to break up the relationship between J. J.’s sister Susie and jazz musician Steve Dallas. Later, at the club where Steve performs, Sidney argues with his uncle and Steve's manager, Frank D’Angelo, who had promised him that Steve and Susie had broken up. Upon learning from cigarette girl Rita that Susie is awaiting Steve in back, Sidney interrupts the two as they celebrate their recent engagement, incurring Steve’s anger. Steve, who values integrity above all else, accuses Sidney of “scratching for information like a dog.” Inside, Rita appeals to Sidney to help her retain her job, which is at risk because she refused to sleep with columnist Leo Bartha, who then ordered her to be fired. Sidney secures a date with Rita, then follows Susie into a cab, where the meek nineteen-year-old questions his relationship with J. J., calling him “a trained poodle.” While reassuring Susie that he considers J. J. a close friend, Sidney confirms the information that Susie and Steve are engaged, then races to J. J.’s customary booth at the 21 Club to inform him. J. J. is dining there with Senator Harvey Walker, starlet Linda James and manager Manny Davis, and when Sidney joins them against J. J.’s wishes, the columnist excoriates him, forcing Sidney to accept the abuse with a smile. When Walker tries to help, pointing out that columnists need press agents to furnish the necessary gossip, J. J. turns his lacerating gaze to the senator, humbling him by stating that he should not travel so openly with Linda, his mistress. Sidney follows J. J. outside, where the columnist greets his informer, police lieutenant Harry Kello, who is long indebted to J. J. for petitioning the mayor to save his job after Kello beat a suspect severely. After Sidney reveals Susie’s engagement, J. J. allows him one more chance to destroy the relationship, stating that Susie is all he has. Desperate to protect his livelihood, Sidney vows that “the cat’s in the bag and the bag’s in the river.” He goes to Toot Shor’s club, where Bartha, J. J.’s main competitor, is dining with his wife Loretta. Sidney threatens to reveal Bartha’s dalliance with Rita to Loretta unless the columnist prints an item stating that Steve is a Communist who smokes marijuana, but despite Sidney’s machinations, Bartha calls his bluff, telling Loretta the truth and calling J. J. a disgrace. Sidney then petitions columnist Otis Elwell, who agrees to print the item if Sidney will fix him up with an “available” woman. To that end, Sidney brings Otis to his scheduled rendezvous with Rita, who balks at the implications of the introduction, until Sidney wheedles her into accepting, stating that Otis can help save her job as well as help him save face with J. J. After Sidney leaves, Rita, who has just told Sidney she is “not that kind of girl,” reminds Otis that they slept together years earlier. The next morning, Sidney visits J. J.’s office, where the secretary, Mary, admonishes him for his sleazy tactics but nonetheless allows him to see J. J.’s column before it is printed. Noting an item promoting comedian Herbie Temple, Sidney then goes to Herbie, hoping to win his business, and pretends to call J. J. and arrange for the publicity. Back at Sidney's office, Frank and Steve are waiting, sure that the “smear” in Otis’ column came from Sidney. Sidney allays their suspicion with his customary outraged defensiveness, then, upon hearing that Steve has been fired, secretly calls J. J. and instructs him to order the club owner to rehire the musician, thus winning Susie’s trust. When Susie, horrified after seeing the article, enters the Hunsecker home, J. J. imperiously chastises the terrified girl for not coming to him with her problems. Susie, suspicious and chafing under her brother’s tight control, finds the strength to ask J. J. to get Steve his job back. J. J. complies but asks Steve to meet him at the radio station. Before the meeting, Sidney advises J. J. to bait Steve into causing a scene, hoping to poison Susie against him. Noting Sidney's delight with his devious plan, J. J. calls him “a cookie full of arsenic.” Sidney then joins with J. J. to taunt the upright musician, prompting Steve to ask Susie what she wants. When the overwhelmed girl flees the room, Steve breaks down and rebukes J. J. as a “national disgrace” full of “phony patriotism.” He storms out, after which J. J. forbids Susie to see him again. That night, Sidney joins J. J. at 21 and is taken aback to discover that the columnist now plans to destroy Steve’s career. Sidney balks at J. J.’s command to plant marijuana on the musician, stating he can accept a dog collar but not a noose, but after J. J. offers to let Sidney write his column for three months while he vacations with Susie, Sidney’s greed prevails and he accepts the job. Later, Susie breaks up with Steve, hoping this will save him from further attacks by J. J., but as soon as Steve finishes work that night, Kello arrests him, beating him in the process. Sidney is getting drunk while toasting his “favorite perfume—success” when he receives a message asking him to meet J. J. at his house. There, Susie, who has learned about Steve’s arrest, is planning to commit suicide, hoping J. J. will forever detest Sidney for driving her to desperation. Sidney downplays the threat, berating the girl for “thinking with her hips,” an improvement, he says, over her typical incompetence. When Susie tries to throw herself over the balcony, Sidney barely manages to rescue her. Just then, J. J. enters and, upon spotting Sidney holding a negligee-clad Susie, attacks the publicist, who realizes that it was not J. J. but Susie who called him to the house. To save himself, Sidney proclaims that Steve’s arrest was J. J.’s idea, after which the columnist calls Kello and orders Sidney’s arrest for planting the marijuana. Sidney runs out, vowing to reveal all he knows, as Susie packs her belongings. J. J. begs her to stay, but she coolly informs him she would rather die than live with him. As Kello beats Sidney and J. J. stares into his empty home, Susie strides to the hospital to join Steve.