An honest police captain vows to bring down a powerful bootlegger who is protected by corrupt politicians and judges.
An honest police captain named McQuigg becomes a tough rival to a powerful bootlegger named Scarsi, even though McQuigg's pinches never stick because Scarsi and his organization control the corrupt politicians and judges. When Scarsi can't scare McQuigg off, he gets him transferred to a quiet police precinct in the suburbs, but McQuigg continues their war of words via a pair of wisecracking newspaper reporters. Then McQuigg catches a huge break when Scarsi's younger brother gets picked up for a hit and run accident in his precinct, putting in motion a complex plan to bring down the mobster using the reporters, a nightclub singing gold digger, the upcoming elections and Scari's own organization.—TimeNTide
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.