Chicago Police Department officer James "Mac" McQuigg tries to keep the peace in Chicago during the
Prohibition gang wars but is hampered by massive
corruption. After a shootout McQuigg manages to arrest mob boss Nick Scarsi's henchman Spike Corcoran, the political boss "The Old Man" arranges to have all charges dropped. After a birthday party for Nick Scarsi's younger brother Joe Scarsi ends in a shootout in which Nick Scarsi kills Corcoran, McQuigg arrests Nick Scarsi for murder but is forced to release him after being unable to find the murder weapon. Although McQuigg vows to bring down Nick Scarsi, he gets transferred to "the sticks" of the 28th precinct. After Joe Scarsi is arrested for a hit-and-run accident, McQuigg convinces his girlfriend Helen Hayes to implicate him. Nick Scarsi arrives and shoots the witness Patrolman Johnson, and McQuigg arrests him again for murder. When Nick Scarsi's attorney arrives with a writ of
habeas corpus to free him, McQuigg rips it up and imprisons him as well. Hayes falls in love with cub reporter Dave Ames, and tricks Nick Scarsi into confessing to keep him from killing Ames. With Nick Scarsi implicated in a crime, "The Old Man" and District Attorney Welch's
political machine turn on Nick Scarsi in order to remain in power at the upcoming municipal election. They trick him into attempting to escape and trying to shoot McQuigg with an empty gun before killing him themselves. ==Cast==