Hank (John Mack Brown) and Carl (Clark Gable), two reporters, set out to investigate the gangland killings. When Scorpio sees them hanging around his café, he hires Anne (Jean Harlow) as a cashier to interest them in her and keep them away from him.  Six leading businessmen, a group of reformers known only as "The Secret Six," ask Hank to get evidence against the gang.  He finds the gun which Scorpio used for his killing, but is followed when discovered.  Anne learns that he has the murder weapon and catches up with him on a subway train.  Her attempt to warn him proves useless, since he is murdered.  Angered by the murder, Anne cooperates with the law in bringing Scorpio to trial, but Scorpio is acquitted by a fixed jury and has her kidnapped.  Carl learns where Anne is being held but is captured himself when he arrives there. The reformers and the police raid the hideout while Carl gets Anne to safety. Scorpio attempts to flee with Newton (Lewis Stone), his lawyer and the brains of the organization. In an argument over splitting the cash they are carrying, Scorpio shoots Newton who, before he dies, repays Scorpio in kind.

Jean's first film with Gable and Beery. Both Jean and Gable were to become two of Hollywood's biggest stars only a year later.

What the critics said about The Secret Six:

New York Times (Mordaunt Hall)
"Jean Harlow, the ash-blonde of several other such tales, once again appears as the girl in the case...The picture moves along swiftly and the dialogue is quite well written."

New York Daily Mirror (Bland Jobaneson)
"Miss Jean Harlow plays Beery's girl friend, a plausible character softened by love for the reporter...The Secret Six is another neat gang melodrama, genuinely thrilling."

New York Post (Thornton Delehanty)
"The picture is unusually well directed and it moves with a pulsating speed...The acting, too, is generally on a high level."