After New York City printer Max Borg is murdered, District Attorney Walker, who is assigned to the case, learns that Borg, who had recently been exposed as the printer of propaganda posters for a race hate group called "The Crusaders," was apparently silenced by them. When an article about the group appears in a local newspaper, Walker's deputy, Howard Malloy, visits the author, Charles Riggs, who is also his sister Caroline's fiancé. Later, Charlie is followed home by a mysterious figure, who knocks him unconscious and pushes him out of his high-rise window. After Caroline finds a propaganda poster inside Charlie's room and shows it to Howard, he notices the words "Sigmund Kosterich, Rembrandt Studios" printed on the back. Howard goes to Kosterich's shop, posing as a potential customer, but Kosterich insists he does not print posters. Before leaving, Howard admires Kosterich's painting of a lovely singer named Barbara Whitfield. When a man follows Howard home, Howard draws his gun, grabs the man's wallet and learns that his name is Miller. Inside the wallet, he finds a newspaper advertisement for Barbara's nightclub act and a card with an address and the words "See the Angel" printed on it. Howard goes to the address, which turns out to be the headquarters of the Mohawk Political Club. There, he introduces himself to "The Angel," Angelo Agostini, who offers to help him win a promotion to special prosecutor. Later, when Howard's friend, socialite Grace Hartley, hears Howard's name linked to Angel's, she warns him against associating with unsavory characters. Howard attends a party at Grace's house, then leaves after receiving a message from his partner, Tommy Quigley. After her show at the Blue Angel nightclub, Barbara meets Howard, and although she is Angel's sweetheart, Howard kisses her. When Angel sees Barbara with Howard, he becomes jealous and orders her to break it off with him. Later, Barbara tells Howard about The Crusaders' racist agenda, and when he tries to kiss her, she surmises that he is only after information and pushes him off the couch. Howard is knocked unconscious when his head hits the coffee table, and while he is unconscious, Grace, the secret head of The Crusaders, arrives, shoots Barbara to death and escapes. Howard revives, and when Kosterich shows up, Howard assumes he is the murderer. Kosterich blames Grace, who unknown to him, is eavesdropping in the hallway outside, then tells Howard that he found evidence of her involvement with The Crusaders while painting a portrait at her house. When Grace overhears Kosterich say that he has hidden the evidence behind one of his paintings at the museum, she rushes out, followed by Angel and Miller, who is also known as "Knuckles." At the museum, Grace knocks out the night watchman, while Howard phones Quigley and tells him to come to the museum. After Howard and Kosterich arrive and find the watchman, Howard goes after Angel, while Kosterich creeps up behind Grace. Howard then shoots Angel, and Grace shoots Kosterich. When Miller arrives and fires at Howard, Kosterich grabs Howard's gun and shoots Grace. Just then, several squad cars arrive at the scene, and Caroline is so relieved to see that her brother is unhurt that she kisses him.
