A distinguished gang of six high-finance racketeers, who include among themselves a judge, frame young assistant district attorney Norman Craig on a bribery charge after Craig gains evidence revealing their scheme to steal millions of dollars. His fiancée, Ruth Knowles, could save him by testifying that she spent the night with him, but she is advised against doing so. While Craig is in prison serving a twenty-year sentence, Ruth marries the leader of the gang, James Gordon, unaware of Gordon's part in the frame-up. When gang member Vickers becomes conscience-striken and threatens to reveal the frame-up, he is set up to be arrested on a robbery charge and sent to the same prison where Craig resides. They become friends, and after Vickers is shot during an escape attempt, he confesses the scheme on his deathbed. Craig is released because of the confession and promoted to first assistant district attorney. Although he knows who framed him, Craig is unable to prove his convictions. After the chief of police promises him absolute freedom for thirty days to obtain evidence, Craig assumes the identity of "The Avenger" and begins to terrorize the conspirators one by one using an airplane, Mills bombs (a type of hand grenade used by the Allies during World War I) and machine guns. Gordon kills one gang member, who shows signs of weakening, and after three others mysteriously disappear, Gordon, the only member left, is driven nearly insane with fear. When Gordon is found dead after Ruth has given him pills to calm him, Gordon's diary is found to reveal that Ruth still loves Craig. She is assumed to have killed her husband until Craig proves that Gordon committed suicide so that Ruth would be charged with murder. Although Ruth believes that Craig murdered Gordon, he abducts her and shows her that he has been keeping the three gang members who have disappeared imprisoned in a shack under an armed guard to obtain their confessions. After the gang are turned over to the police, Craig and Ruth are reunited.